Wiring transfer sheet and method for producing the same, and wiring board and method for producing the same

ABSTRACT

A wiring transfer sheet including a carrier base and a wiring layer formed thereon is produced so that an exposed area of a surface of the carrier base on which the wiring layer is formed has a plurality of concavities. By transferring the wiring layer to an electrically insulating substrate with this wiring transfer sheet, convexities which are complementary to the concavities are formed on the electrically insulating substrate. The convexities improve adhesion between a wiring board and a resin stacked thereon. Therefore, the wiring board thus obtained has surface coplanarity suitable for mounting a semiconductor bare chip and an electronic component as a whole, and a microscopical surface structure which adheres to a material stacked thereon.

[0001] This application is a Divisional Application of Ser. No.10/420,876 filed Apr. 23, 2003 which is currently pending.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] The present application claims a priority under 35 U.S.C. §119 toJapanese Patent Application No. 2002-124407 filed on Apr. 25, 2002,entitled “Wiring transfer sheet and method for producing the same, andwiring board and method for producing the same”. The contents of thatapplication are incorporated herein by the reference thereto in theirentirety.

FIELD OF THE INVENTION

[0003] The present invention relates to a wiring transfer sheet which isused for forming a wiring of a wiring board and to a method forproducing the same, and further relates to a wiring board which isproduced by using the wiring transfer sheet and a method for the wiringboard by using the wiring transfer sheet.

BACKGROUND OF THE INVENTION

[0004] Recently, a multilayer wiring board on which semiconductor chipssuch as an LSI and so on can be mounted at a high density has been usednot only in the filed of industrial apparatus, but also in the field ofhousehold electric appliances, as a result of miniaturization andimprovement in performance of electronics devices. For this reason, acheaper multilayer wiring board is required. Further, the market alwaysrequires a multilayer board wherein a plurality of wiring pattern layerswith a finer wiring pitch are electrically connected with a higherinterconnection reliability.

[0005] In order to meet the requirement, a multilayer board wherein aninner via hole connection method is employed for interlay connectioninstead of a through-hole plating which was mainly employed, has beendeveloped and practically used. According to the inner via holeconnection method, interlayer connection between any electrodes of themultilayer print-wiring board can be obtained at any position of awiring pattern. This multilayer board is called an All LayersInterstitial Via Hole (IVH) structure resin multilayer wiring board (seeJapanese Patent Kokai (Laid-Open) Publication No. 6-268345). Byemploying this multilayer wiring board, it is possible to make aconnection only between the desired wiring layers by filling the viahole with a conductive substance. Further, in this multilayer wiringboard, it is possible to realize miniaturization of the board size andhigh density mounting since the inner via hole can be formed just undera component land.

[0006] In order to realize an interlayer connection with a higherdensity, there has been proposed a wiring board wherein two wiringlayers formed on both surfaces of an electrically insulating substrateare electrically connected with a conductive paste which is filled ininner via holes, and at least one wiring layer is embedded in anadhesive layer. In addition, a method for producing the wiring board hasbeen proposed, in which the wiring layer is embedded in the adhesivelayer by transferring the wiring layer formed on a support base (seeJapanese Patent Kokai (Laid-Open) Publication No.2000-77800). Byemploying this constitution, a high reliability is obtained even if thesize of the inner via hole is small. Further, there has been proposed atransfer medium with a fine wiring pattern which is suitable forproducing a high-density multilayer wiring board (see Japanese PatentPublication No. 3172711). A wiring transfer sheet which is suitable forforming a wiring layer is also disclosed in Japanese Patent Kokai(Laid-Open) Publication No.2000-154354.

[0007] The technique of forming the wiring layer with the wiringtransfer sheet has been employed in the production of the wiring boardas a useful method for forming the wiring. In the following, an exampleof the method for forming a wiring layer with a wiring transfer sheet isdescribed referring to FIG. 16.

[0008] FIGS. 16(a) to (c) shows cross-sectional views illustrating themain steps in a method of forming a wiring layer. FIG. 16(a) shows astate in which wiring transfer sheets 1203 are superposed on bothsurfaces of an electrically insulating substrate 1204. FIG. 16(b) showsa step of transferring wiring layers 1202 of the wiring transfer sheets1203 to the electrically insulating substrate 1204. FIG. 16(c) shows astep of removing support bases 1201 so as to obtain a wiring board.

[0009] In FIG. 16(a), the wiring transfer sheet 1203 is constituted bythe support base 1201 and the wiring layer 1202 which is formed on thesupport base in a predetermined pattern. The wiring transfer sheet 1203is produced by laminating a copper foil on an aluminum foil to obtain acomposite foil followed by etching the copper foil selectively in adesired pattern, as described in Japanese Patent Publication No.3172711. An enlarged view of Area A in the vicinity of the wiring layerof this wiring transfer sheet 1203 is shown in FIG. 16(d). As shown inFIG. 16(d), in the wiring transfer sheet, an exposed area of a surfaceof the support base 1201 (i.e. a surface which contacts the electricallyinsulating substrate) is flat. This is because the aluminum foil has aflat surface.

[0010] In FIG. 16(a), the electrically insulating substrate 1204 (towhich the wiring layer is to be transferred) has through holes 1205which are filled with a conductive paste 1206. A porous substrate whichcan be compressed, or a three-layer substrate wherein a core film issandwiched with adhesive layers is used as the electrically insulatingsubstrate 1204. The through holes 1205 are formed by laser processingusing a carbon dioxide laser, an excimer laser or a YAG laser. The laserprocessing is generally employed for forming through holes since it isexcellent in productivity.

[0011] Next, as shown in FIG. 16(b), the wiring transfer sheet 1203 isadhered to the electrically insulating substrate 1204 by heating andpressurizing, and then the wiring layer 1202 is transferred to andembedded in the electrically insulating substrate 1204. The electricallyinsulating substrate 1204 contains a thermosetting resin which is curedupon heating and pressurization so as to adhere to the wiring layer.Further, the conductive paste 1206 filled in the through holes 1205 iscompressed by embedding the wiring layer 1202. Compression of theconductive paste 1206 makes the density of the conductive particles inthe conductive paste high. Thus, the electrical connection between thewiring layers 1202 is ensured.

[0012] Next, the support base 1201 is dissolved and removed by etchingwhereby a wiring board which has wiring layers on both surfaces isobtained as shown in FIG. 16(c). Etching is conducted using as anetchant chemicals which selectively dissolve only the support base 1201and do not dissolve the wiring 1202. FIGS. 16(e) and (f) show enlargedviews of Areas B and C shown in FIG. 16(c), respectively. As shown inFIG. 16(e), an exposed area of a surface of the electrically insulatingsubstrate 1204 becomes flat as a result of transferring the surfaceshape of the support base 1201. As shown in FIG. 16(f), the surface ofthe wiring layer 1202 also becomes flat. This is because the face whichcorresponds to the surface of the wiring layer 1202 reflects the surfaceshape of the support base 1201 which the wiring layer 1202 has contactedbefore transferring. A semiconductor bare chip is advantageously mountedon the wiring board having such a flat surface, and thereby an excellentinitial mounting characteristic is ensured.

[0013] As the flatness of the surface of the wiring board increases, theinitial mounting characteristic becomes better, while the adhesivenessof the wiring board to a substance (e.g. a resin) which is laminated onits surface disadvantageously becomes lower. The substances to belaminated on the surface of the wiring board are, for example, a sealingresin which is used upon mounting a semiconductor bare chip, and asolder resist for protecting a solder which is used upon mounting anelectrical component. In a case where the adhesion between thesematerials and the surface of the wiring board is bad, interfacialexfoliation tends to occur due to stress caused by heating or bending.Similarly, when a multilayer wiring board is obtained by laminatinganother electrically insulating substrate on the double-faced wiringboard produced according to the steps shown in FIG. 16, the highflatness of the wiring board lowers the adhesiveness of the electricallyinsulating substrate to the wiring board, which tends to causeinterfacial exfoliation between the electrically insulating substratesand interfacial exfoliation between the insulating substrate and thewiring layer (the copper foil) of the wiring board. In any case, theoccurrence of the interfacial exfoliation causes mounting failure orcontact failure, so that the property of a product in which the wiringboard is incorporated is adversely affected.

[0014] As described above, the wiring board obtained by using theconventional wiring transfer sheet has excellent surface flatness,although there is a problem in that it is difficult to ensure theadhesiveness of the wiring board to the resin laminated thereon due tothe high surface flatness. The present invention has been made inconsideration of these circumstances, and an object thereof is toprovide a wiring transfer sheet that enables production of a wiringboard which has a surface flatness macroscopically suitable for mountinga semiconductor bare chip or a electronic component thereon, but whichalso has a surface structure to which a resin to be laminated thereonmicroscopically adheres well. Further, an object of the presentinvention is to provide a wiring board which is produced by using thewiring transfer sheet, wherein at least an exposed area of a surface ofan electrically insulating substrate has a surface flatnessmacroscopically suitable for mounting a semiconductor bare chip thereon,while it also has a surface structure to which a resin to be laminatedthereon microscopically adheres well.

SUMMARY OF THE INVENTION

[0015] In order to achieve the object, the present invention provides awiring transfer sheet including a carrier base and a wiring layer formedon the carrier base, wherein, at least an exposed area of a surface ofthe carrier base on which the wiring layer is formed is a rough surfacewhich is for forming another rough surface complementary to the formerrough surface on an object to which the wiring layer is to betransferred. This wiring transfer sheet is for obtaining a wiring boardby transferring the wiring layer to an electrically insulatingsubstrate. Therefore, the object to which the wiring layer is to betransferred (which is merely referred to as an “object”) is anelectrical substrate for a wiring board.

[0016] By using this wiring transfer sheet, at the same time when thewiring layer is transferred to the electrically insulating substrate toform a surface of a wiring board which has the wiring layer, at least anarea of the surface on which area no wire (i.e. no wiring material)lies, can be made a rough surface. When the surface of the wiring boardis made a rough surface, the contact surface area of the wiring board(that is, the surface area which contacts a resin to be laminatedthereon) is increased, so that the adhesiveness of the resin to thewiring board is improved. Therefore, the wiring board produced using thewiring transfer sheet of the present invention adheres well to the resinto be applied thereto.

[0017] In a wiring transfer sheet of the present invention, a “carrierbase” is a sheet-like member which holds a wiring layer until the wiringlayer is transferred to an electrically insulating substrate. In thewiring transfer sheet, the “wiring layer” is made of a conductivematerial, and is patterned so that a predetermined wiring pattern isformed in a wiring board.

[0018] The wiring layer is formed on one of the main surfaces of thecarrier base (that is, one of the two large surfaces of the sheet). Inthis specification including the following description, a main surfaceof the carrier base is merely referred to as a “surface”, and the mainsurface of the carrier base on which the wiring layer is formed isreferred to as a “surface of a carrier base on which a wiring layer isformed.” With respect to other sheet-like members, the main surfaces aremerely referred to as a “surface.”

[0019] The wiring transfer sheet is characterized in that at least anexposed area of a surface of the carrier base on which the wiring layeris formed is a rough surface. Here, the term “at least” is used in thesense that it includes an embodiment wherein only the area where thecarrier base is exposed is a rough surface, and an embodiment whereinthe entire surface of the carrier base (including an interface betweenthe carrier base and the wiring layer) is a rough surface. The “roughsurface” means a surface which has concavities and convexities. Theconcavities and convexities which constitute the rough surface include avariety of embodiments. The shape of each convexity or each concavitymay be any one of a pointed shape (a conical shape or a pyramid shape),a column shape, a wrinkle shape, a ribbed shape, a bump shape, and amushroom shape. Further, the rough surface includes an embodiment whichonly has concavities formed on a substantially flat surface, and anembodiment which has only convexities formed on a substantially flatsurface. When transferring the wiring layer, the rough surface which isthe exposed area of the surface of the carrier base closely contacts theobject, and then a material of the object flows or softens to deform,which results in formation of another rough surface complementary tothis rough surface of the carrier base on the object.

[0020] In the present invention, it suffices that the shape of the roughsurface which is formed on the object is substantially complementary tothe area where the surface of the carrier base of the wiring transfersheet is exposed, and strict correlation is not required. For example,when the fluidity of the resin contained in the electrically insulatingsubstrate that is the object is small so that the resin does notcompletely reach a bottom surface of a concavity, a convexity which hasa height somewhat smaller than the depth of the concavity may be formed.When a wiring transfer sheet is made by laminating a copper foil havinga rough surface on a resin sheet with the rough surface closelycontacting the resin sheet to roughen a surface of the resin sheetfollowed by etching the copper foil, a wiring material (i.e. copper) maybe left in concavities on an area where the surface of the resin sheetis exposed. In the case where such a wiring transfer sheet is used,convexities formed on an object have a height smaller than the depth ofthe concavities by the thickness of copper left in the concavities. Suchconvexities are regarded as being complementary to the concavities onthe wiring transfer sheet. It should be noted that it is important inthe present invention that the exposed surface of the electricallyinsulating substrate of the wiring board is roughened throughtransferring.

[0021] As described above, the feature of the wiring transfer sheet ofthe present invention is that it serves to roughen the surface of theelectrically insulating substrate. Further, the inventors have foundthat, as to the wiring transfer sheet of the present invention, in acase where the conductive material is left on the area between wireswhere the surface of the carrier base is exposed (specifically in theconcavities) after a desired wiring pattern has been formed by etching,the conductive material is not transferred to the electricallyinsulating substrate. This is also the feature of the wiring sheet ofthe present invention. When a wiring board is produced by bonding aroughened copper foil to a surface of an electrically insulatingsubstrate followed by etching the copper foil so as to form the wiringlayer, copper often remains on an unnecessary area after etching.Particularly, when a wiring pattern is fine, such remaining copperbecomes more marked, and causes a short circuit. In order to preventsuch a problem, overetching is often carried out. Overetching makes awiring layer under a resist narrow, which may cause delamination of theresist. The delamination of the resist may hinder formation of necessarywiring, resulting in a failure to form a desired wiring pattern. Forthis reason, it is necessary to carefully control overetching when thewiring layer is formed on the surface of the electrically insulatingsubstrate by etching. On the other hand, the above-mentioned feature ofthe wiring transfer sheet of the present invention makes it possible toeasily form a wiring layer having a fine wiring pattern on anelectrically insulating substrate without leaving a conductive materialbetween wires unnecessarily.

[0022] The wiring sheet of the present invention is preferably onewherein the exposed area of the surface of the carrier base has aplurality of concavities for forming convexities that are substantiallycomplementary to the concavities on the object. Herein, the term“concavity” is used to mean a portion which is apparently recessed fromother portions and a recess which is formed on a substantially flatsurface. The “portion which is apparently recessed from other portions”is, for example, a particularly deep hollow which exists on the surfacehaving irregularities. Such a portion includes a portion which is shownas a dark portion on a photomicrograph with a magnification of about1,000. On the other hand, the term “convexity” is used to mean a portionwhich apparently protrudes from other portions, and a protrusion whichis formed on a substantially flat surface. The “portion which apparentlyprotrudes from other portions” is, for example, a particularly highprotrusion which exist on the surface having irregularities. Such aportion includes a portion which is observed as a protrusion on aphotomicrograph with a magnification of about 1,000.

[0023] The surface having a plurality of concavities is obtained bysubjecting a substantially flat surface to a) embossing using a male dieembossing die having a plurality of convexities, b) a sandblastprocessing so that a part of the surface is scraped away, or c)electrolytic etching or dry etching. The male die having a plurality ofconvexities includes a metal foil on which particles are depositedthrough electrolytic plating, and an embossing roll.

[0024] Upon transferring a wiring layer to an object, the area havingsuch concavities contacts the object, and then a material constitutingthe object flows into the concavities. Thereafter, the base material ispeeled off. As a result, convexities which are substantiallycomplementary to the concavities are formed on the surface of theobject. The convexities formed on the surface give an anchoring effectby being easily embedded into a resin which is stacked on them. To thecontrary, in the case where a resin is stacked on a surface havingconcavities, it is necessary to lower the melt viscosity of the resin,or to apply a large pressure upon stacking the resin so that the resincan flow into the concavities. That is, the structure of the surfacehaving convexities adheres better to the resin stacked on it than doesthe surface having concavities. For this reason, the exposed area of thesurface of the carrier base is preferably a rough surface having aplurality of concavities so that they can form a surface structurehaving convexities on the object.

[0025] Further, the wiring transfer sheet of the present invention ispreferably one in which the entire surface of the carrier base on whichthe wiring layer is formed has a plurality of concavities, and thewiring layer enters the concavities. When the wiring layer of such awiring transfer sheet is transferred to a surface of an electricallyinsulating substrate, the interface between the wiring layer and thecarrier base is exposed. As a result, the surface of the transferredwiring layer also has convexities which are complementary to theconcavities. In a wiring board, the proportion of the wiring layer on asurface depends on the kind of wiring board. For example, in a wiringboard, an exposed area of a surface of the wiring layer is larger thanan exposed area of a surface of the electrically insulating substrate.When a resin is stacked on the surface of such a wiring board, the areawhere the stacked resin contacts the wiring layer may be larger than thearea where the stacked resin contacts the electrically insulatingsubstrate. In this wiring board, the convexities which exist on thesurface of the wiring layer are convenient for ensuring betteradhesiveness to the resin. Further, the wiring transfer sheet in whichthe wiring layer enters the concavities formed on the carrier baseensures better adhesion therebetween since they engage each other.Therefore, as to the wiring board of this structure, it is generallyunnecessary to combine the carrier base with the wiring layer using anadhesive agent.

[0026] The concavities on the surface of the carrier base occupy 50 to98% of at least the exposed area of the surface. If the proportion ofthe concavities on the carrier base is small, the proportion of theconvexities on the object is also small, and therefore theabove-mentioned effect is not obtained.

[0027] Each concavity on the surface of the carrier base preferably hasa diameter in the range of 0.5 to 5 μm. Herein, a “diameter” correspondsto the length of the longest line of lines each of which connects twoarbitrary points on the concavity contour on the surface of the carrierbase. The concavity contour on the surface of the carrier basecorresponds to the contour of the concavity viewed from top. Theconcavities whose diameters are in the above range may be a part of orall of the concavities which exist on the surface of the carrier base.Therefore, some of the concavities may have a larger diameter than theupper limit of the above-mentioned preferable range. A concavity with alarger diameter is viewed, for example, as a type of concavity in whichsome concavities range. A part of or all of the convexities formed bysuch concavities each have a diameter in the range of 0.5 to 5 μm at itsbasis. Here, a “basis” means a plane on which the bottom ends (i.e.starting points) of the convexity exist. In the case where the bottomends of a convexity are not on a plane which is parallel to a surface ofan object, its basis is an area which is defined by crossing a planeparallel to a surface of the object on which the lowest bottom endpasses, and its trajectory (i.e. vertical lines) is obtained by shiftingother bottom ends in a vertical direction (i.e. the thickness direction)toward the surface of the object. Here, a “plane parallel to a surfaceof an object” means a plane parallel to a flat surface obtained byleveling the concavities and convexities which exist on the surface ofthe object (an electrically insulating substrate), and it is a verticalplane (perpendicular) with respect to a thickness direction of theelectrically insulating substrate.

[0028] The concavity preferably has a depth in a range of 0.5 to 5 μm.The convexity formed by such a concavity has a height in a range of 0.5to 5 μm. The height of the convexity is the shortest distance betweenthe basis and the top of the concavity.

[0029] The diameter Su of a concavity on the surface of the carrier baseand the depth D of the concavity are schematically shown in FIGS. 14(a)and (b). Su can be regarded as a diameter of the front of the concavity.In the concavity shown in FIG. 14(a), the areas of the sections whichare vertical to the depth direction are not uniform. The top end of theillustrated concavity is on a plane which is parallel to the surface ofthe carrier base. The depth of a concavity whose top end is not on aplane which is parallel to the surface of the carrier base is a distancebetween the bottom of the concavity and a plane which is parallel to thesurface of the carrier base and on which the highest top end (that is,the uppermost top end) passes. A “surface which is parallel to a surfaceof a carrier base” means a plane parallel to a flat surface obtained byleveling the concavities and convexities which exist on the surface ofthe carrier base, and it is a vertical plane (i.e. perpendicular) withrespect to a thickness direction of the carrier base. A convexity whichis formed by the concavity shown in FIGS. 14(a) and (b) is shown in FIG.14(c). As shown in FIG. 14(c), this convexity has a shape which iscomplementary to the concavity. The basis of this convexity correspondsto the dotted line identified by “R”, and its shape and diameter is thesame as those shown in FIG. 14(b). Further, the height of the convexity(i.e. the shortest distance between the basis R and the top T) is equalto the depth D.

[0030] The concavity preferably has a shape of which sections verticalto the depth direction of the concavity are not uniform, and of whichone of such sections having a maximum area exists at an intermediateposition between the surface of the carrier base and the bottom of theconcavity. Examples of such a concavity are shown in FIGS. 15(a) to (c).Each concavity shown in FIG. 15 (that is, a space surrounded by thecarrier base) has an expanded portion between the bottom B and thesurface of the carrier base, and the maximum sectional area is at thepoint m where the concavity expands most. The shape of each concavity(i.e. the shape of space surrounded by the carrier base) is a bud-shape(FIG. 15(a)), a bump-shape (FIG. 15(b)), or a mushroom-shape (FIG.15(c)). These concavities can form convexities which expand at thewaist, such as a bud-shaped, a bump-shaped or a mushroom-shapedconvexity. In other words, each of these concavities can form aconvexity in which a section vertical (perpendicular) to a heightdirection of the convexity (or a thickness direction of a wiring board)is largest at a position between the basis and the top. Such a convexitygives a larger anchoring effect, and therefore the wiring board havingsuch a convexity on its surface adheres more favorably to a resinstacked thereon. Such a convexity can be regarded as one having“undercut” in the field of resin molding, and the undercut contributesto a higher anchoring effect.

[0031] In the concavity as shown in FIG. 15, of the sections which areperpendicular to the depth direction of the concavity, the sectionhaving the maximum area preferably has a diameter in the range of 1 to10 μm. In FIG. 15, the diameter of the section having the maximum area(that is, the diameter at the most expanded point m) is shown by Smax.In the convexities formed by these concavities, a diameter of thesection having the maximum area (that is, the section at the mostexpanded point) is in the range of 1 to 10 μm.

[0032] The wiring transfer sheet of the present invention is identifiedas a wiring transfer sheet including a carrier base and a wiring layerformed thereon. At least an exposed area of a surface of the carrierbase on which the wiring layer is formed has a surface shape that isformed by pressing a metal foil having a plurality of convexities formedby electrolytic plating against the surface of the carrier base whilethe convexities contact the surface of the carrier base, followed byremoving the metal foil. Such a surface shape is used for forminganother surface shape complementary to the former surface shape on asurface of an object to which the wiring layer is to be transferred. Insuch a wiring transfer sheet, the exposed area of the surface of thecarrier base has a surface shape which results from the convexitiesformed on the surface of the metal foil, and therefore, such a wiringtransfer sheet gives the same effect as that of the above-mentionedwiring transfer sheet. The exposed area of the surface of the carrierbase is a rough surface, and more specifically a rough surface having aplurality of concavities as described above. The convexities formed onthe object by the use of this wiring transfer sheet are substantiallythe same as the convexities on the surface of the metal foil, since theconcavities are complementary to the convexities on the surface of themetal foil.

[0033] The convexities formed on the surface of the metal foil byelectrolytic plating generally have a bump-shape or a cloud-shape whichis formed of fine particles (for example, round particles with adiameter of 0.1 μm to 4 μm) which are deposited so that they areflocculated and/or piled up. The shape and size of the convexity dependon the condition of electrolytic plating. Therefore, it is preferablethat the convexities on the surface of the metal foil are formed byelectrolytic plating under a condition appropriately selected so thatdesired concavities can be formed on the exposed area of the surface ofthe carrier base depending on the shape of the convexities to be formedon the object.

[0034] The wiring transfer sheet of the present invention is alsoidentified as a wiring transfer sheet including a carrier base and awiring layer formed thereon, wherein the wiring layer is to betransferred to an object. The exposed area of a surface of the carrierbase is for making an average of ten point heights of irregularities Rzin the range of 2 to 12 μm within an area of the object, which areacontacts the exposed area. Such a wiring transfer sheet makes thesurface of the wiring board entirely flat, while making it a surfacehaving concavities and convexities microscopically. The wiring boardhaving such a surface has an excellent initial mounting characteristic,and adheres well to a material stacked thereon.

[0035] The carrier base of the wiring transfer sheet is preferably madefrom a material which is not compatible with a material of an object,that is, an electrically insulating substrate for a wiring board. Thecarrier base of such a material is easily removed from the electricallyinsulating substrate after the wiring layer has been transferred. Thematerial for the carrier base is selected depending on the kind of theobject (that is, the material of the electrically insulating substrate).When the electrically insulating substrate is, for example, onecontaining an epoxy resin, the carrier base is preferably made of afluorine-containing resin. Since the fluorine-containing resin exhibitsan excellent release-ability as to the electrically insulating substrateand has an excellent heat resistance, it does not decompose by heatingand pressurization and is not compatible with the electricallyinsulating substrate. Therefore, the wiring transfer sheet having thecarrier base made of the fluorine-containing resin makes it possible toroughen a surface of the electrically insulating substrate with ease.Particularly, when the carrier base has fine concavities on the exposedarea of the surface, such a wiring transfer sheet makes it possible toform fine convexities on a surface of the electrically insulatingsubstrate with ease.

[0036] In the wiring transfer sheet of the present invention, thecarrier base may be a laminate which is composed of a plurality oflayers wherein a surface on which the wiring layer is to be formed is asurface of a layer made from a material which is not compatible with theelectrically insulating substrate. In the case where the carrier base ismade of a combination of a plurality of layers whose material aredifferent from each other, the release-ability of the carrier base isensured while the strength and handling property of the wiring transfersheet are improved. Specifically, the carrier base is preferably made ofa metal foil such as a copper foil and a resin sheet.

[0037] In the wiring transfer sheet of the present invention, the wiringlayer has concavities and convexities on a surface which is not incontact with the carrier base. The surface of the wiring layer which isnot in contact with the carrier base is a surface which contacts asurface of an object (that is, an electrically insulating substrate fora wiring board) upon transferring. When the surface of the wiring layerwhich is in contact with the object has concavities and convexities, theinterface area between the object and the wiring layer becomes larger,resulting in the improvement of the adhesion between the wiring layerand the electrically insulating substrate. The surface of the wiringlayer which is not in contact with the carrier base preferably hasconvexities. In that case, an anchoring effect given by the convexitiesstrengthens the adhesion between the wiring layer and the electricallyinsulating substrate in the wiring board.

[0038] In the wiring transfer sheet of the present invention, thecarrier base and the wiring layer may be made of metals, each of whichis selectively removed from the other. Such a wiring transfer sheetmakes it possible to carry out the step of removing the carrier base by,for example, selective etching, after the wiring layer has beentransferred. Selective etching makes it possible to remove the carrierbase easily without causing stress in the carrier base. Therefore,selective etching effectively prevents the rough surface, particularly afine convexity which is formed on the electrically insulating substrate,from breaking during the removal of the carrier base.

[0039] In the wiring transfer sheet of the present invention, a junctionlayer is preferably formed between the carrier base and the wiring layerfrom a material which is different from that of the wiring layer. Thejunction layer is specifically made of a metal or a metal oxide. Thejunction layer strengthens the adhesion between the wiring layer and thecarrier base. The junction layer is useful in the case of forming a finewiring pattern which tends to exfoliate from the carrier base.

[0040] In the wiring transfer sheet of the present invention, thecarrier base is preferably made of a material through which a visibleray can pass. In the case where the carrier base is made from such amaterial, alignment markers of the wiring transfer sheet and alignmentmarkers of the object are visible from one side at the time ofsuperposing the wiring transfer sheet on the object. That is, thesealignment markers can be recognized by one recognition system (such as acamera). Using one recognition system inhibits the lamination accuracyfrom lowering due to the difference in coordinates among a plurality ofrecognition systems, resulting in an improvement of lamination alignmentaccuracy of the wiring transfer sheet.

[0041] In the wiring transfer sheet of the present invention, the wiringlayer may be buried in the carrier base. Here, the expression “a wiringlayer is buried in a carrier base” means a state in which 50% or more ofthe thickness of the wiring layer is in the carrier base. By using sucha wiring transfer sheet, the wiring layer is transferred so that itprotrudes from the surface of the object, that is, so that the surfacesof the wiring layer and the electrically insulating substrate are notflush. When a semiconductor bare chip is mounted on a wiring board fromwhich a wiring layer is protruding, the gap between the electricallyinsulating substrate and the semiconductor bare chip is wider. Into thewide gap, a sealing resin which is injected after mounting easily flows.When the sealing resin flows well into the gap, the reliability ofmounting is improved. Therefore, the wiring transfer sheet in which thewiring layer is buried in the carrier base is preferably used, forexample, when the wiring layer is formed on a surface of theelectrically insulating substrate which is to be a mounting surface.

[0042] The present invention also provides a method for producing theabove-described wiring transfer sheet of the present invention. Threemethods are provided for producing the wiring transfer sheet of thepresent invention.

[0043] A first method for producing a wiring transfer sheet of thepresent invention includes: superposing on a surface of a carrier base asheet of wiring material which has a rough surface while the roughsurface contacts the surface of a carrier base. On the surface of thecarrier base, another rough surface complementary to the rough surfaceof the sheet of the wiring material is formed. A wiring layer with apredetermined wiring pattern is formed by etching the sheet of thewiring material. A sheet of a wiring material (which is merely referredto as a “wiring material sheet”) which has a rough surface contacts acarrier base, and then another rough surface complementary to the roughsurface of the wiring material sheet is formed on a surface of thecarrier base by, for example, pressurization. According to this method,a surface of the carrier base is easily roughened. A part of the roughsurface formed in this manner is exposed by etching the wiring materialsheet.

[0044] In this method, when the wiring material sheet which has aplurality of convexities on its surface is used, and the convexities areburied in the carrier base, a plurality of concavities complementary tothe convexities can be formed on a surface of the carrier base. By usingsuch a wiring material sheet, the convexities of the wiring layer adhereto the carrier base strongly by virtue of an anchoring effect, resultingin a structure in which the wiring layer enters the concavities on thesurface of the carrier base in the wiring transfer sheet. Therefore,according to this method, the necessity of using an adhesive agent forbonding the carrier base and the wiring layer is eliminated.

[0045] A second method for producing a wiring transfer sheet of thepresent invention includes forming a wiring layer with a predeterminedpattern on a surface of a carrier base, and roughening an exposed areaof the surface of the carrier base on which surface the wiring layer isformed, by a roughing treatment. According to this method, the exposedsurface of the carrier base is made any rough surface by appropriatelyselecting a condition of the roughening treatment. The rougheningtreatment is preferably carried out so that a plurality of concavitiesare formed on the exposed surface of the carrier base.

[0046] A third method for producing a wiring transfer sheet of thepresent invention includes forming a wiring layer by depositing a metalthrough metal plating, on a rough surface of a carrier base. Accordingto this method, it is possible to use a carrier base on which a roughsurface has been formed so that its profile becomes a predetermined one,which facilitates designing a surface shape of a wiring board asdesired. Further, since a predetermined wiring pattern is deposited byplating, a finer wiring can be made. The rough surface of the carrierbase preferably has a plurality of concavities.

[0047] In another aspect, the present invention provides a wiring boardwhich is obtained by using a wiring transfer sheet of the presentinvention. A wiring board of the present invention is a wiring boardobtained by transferring a wiring layer of a wiring transfer sheet ofthe present invention to a surface of an electrically insulatingsubstrate. As to a surface of the wiring board which surface has thewiring layer, at least an exposed surface (i.e. an exposed area of asurface) of the electrically insulating substrate is a rough surface.Here, the term “at least” is used in the sense that it includes anembodiment in which only the area of a surface of a wiring board wherethe electrically insulating substrate is exposed (that is, the area onwhich wire is not disposed) is a rough surface, and an embodiment inwhich, as to a surface of a wiring board, the exposed area of theelectrically insulating substrate and the surface of the wiring layerare rough surfaces. In this wiring board, a surface coplanarity which isrequired for mounting a semiconductor chip and an electronic componentat a high density is realized, while the adhesiveness of the wiringboard to a material laminated thereon is ensured by the rough surface.

[0048] More specifically, the wiring board of the present invention isone which is produced by a wiring transfer sheet in which an exposedarea of a surface of a carrier base on which surface a wiring layer isformed has a plurality of concavities. In other words, the wiring boardis one in which, as to a surface of the wiring board which surface hasthe wiring layer, at least an exposed surface of the electricallyinsulating substrate has a plurality of convexities. The meaning of “atleast” is as described above. Such a wiring board adheres well to aresin laminated thereon since the convexities give an anchoring effectwhen the resin is laminated on the surface of the wiring board. In thisspecification, an electrically insulating substrate which is included ina wiring board may be referred to as an “electrically insulating layer.”

[0049] The preferable shape and size of the concavity on the exposedsurface of the electrically insulating substrate of the wiring board areas described above in connection with the concavity on the wiringtransfer sheet. Therefore, the detailed description thereof is omittedhere.

[0050] The wiring board of the present invention may be a multilayerwiring board having two or more electrically insulating substrates. Insuch a wiring board, at least one wiring layer is formed using thewiring transfer sheet of the present invention. Of course, it ispreferable that all wiring layers are formed using the wiring transfersheet of the present invention. In the wiring board after the wiringlayer has been formed using the wiring transfer sheet of the presentinvention, the exposed surface of the electrically insulating substrateis a rough surface. Therefore, when another electrically insulatingsubstrate is superposed on this wiring board, adhesion between theelectrically insulating substrates becomes favorable.

[0051] The wiring board of the present invention may be a wiring boardwith a built-in component, in which a component connected with a wiringlayer is embedded in the electrically insulating layer. Such a wiringboard has different functions by the virtue of the component.

[0052] In the case where the wiring board with a built-in component is amultilayer wiring board, the component may extend with in two or moreadjacent electrically insulating substrates. When the component islarge, such a structure is required. As described below, the wiringboard of this structure may be produced by stacking a plurality ofelectrically insulating substrates which are cured to some extent, butnot cured completely. Then, a space (for example, a through hole) inwhich the component is to be placed is formed, and then disposing thecomponent is arranged in the space.

[0053] In the wiring board of the present invention, the electricallyinsulating substrate preferably has through holes which are formed inthe thickness direction of the substrate and which are filled with aconductive paste which electrically connects the wiring layers which areopposite through the electrically insulating substrate. By employingsuch a configuration, the wiring board of the present invention isprovided with stacked via holes in the surface electrically insulatinglayer, which realizes a higher density wiring and makes it possible toensure a larger area for mounting electronic components on the surfaceof the board. The electrically insulating substrate contains a resin asa matrix component. As the resin, a thermosetting resin is generallyemployed from the viewpoint of thermal stability. The resin may be athermoplastic resin. In the case where the electrically insulatingsubstrate contains a thermosetting resin, the resin is cured in a wiringboard when using the board practically. As mentioned below, a wiringlayer in which a part of or all of the thermosetting resin contained inthe electrically insulating substrate is uncured or semi-cured does notfunction at all, or functions incompletely. The wiring board in such astate is referred to as a “wiring board intermediate” in thisspecification.

[0054] In the case where the wiring board of the present invention isprovided with a built-in component, an electrically insulating substratewhich has the built-in component may have the through holes filled withthe conductive paste. Such a wiring board has a configuration wherein alayer with a built-in component has a via that connects wiring layers.

[0055] The present invention also provides a method for producing awiring board of the present invention. As methods for producing thewiring board of the present invention, a first and a second methods areprovided.

[0056] The first method for producing a wiring board of the presentinvention is one in which the step of forming at least one of wiringlayers which are disposed through an electrically insulating substrateon both surfaces of an electrically insulating substrate includes (1)superposing a wiring transfer sheet of the present invention (that is, awiring transfer sheet including a carrier base and a wiring layer formedon the carrier base, wherein at least an exposed area of a surface ofthe carrier base on which the wiring layer is formed is a rough surface)on at least one surface of the electrically insulating substrate whichhas through holes filled with a conductive paste. (2) The wiring layerof the wiring transfer sheet is adhered to the electrically insulatingsubstrate, an exposed area of a surface of the electrically insulatingsubstrate which includes thus transferred wiring layer (that is, an areaof the surface on which area no wire is present) is roughened, throughheating and pressurizing a layered body which consists of the wiringtransfer sheet and the electrically insulating substrate. (3) Thecarrier base of the wiring transfer sheet is removed. According to thismethod, a wiring board which has the above-mentioned features isproduced. In this method, by using a wiring transfer sheet which has aplurality of concavities on the exposed area of the surface of thecarrier base, convexities complementary to the concavities are formed onthe exposed surface of the electrically insulating substrate.

[0057] According to the method, a multilayer wiring board can beproduced efficiently. In a method for producing the multilayer wiringboard, for example, a substrate which contains an uncured thermosettingresin is used as the electrically insulating substrate, and theelectrically insulating substrate on which the wiring transfer sheet issuperposed is superposed on a wiring board or a wiring boardintermediate (an intermediate of a wiring board) in step (1) followed byadhering the electrically insulating substrate to a surface of thewiring board or the wiring board intermediate through heating andpressurization. Here, a wiring board intermediate means a structurewhich has stacked wiring layer(s) and stacked electrically insulatingsubstrate(s), but does not function at all or functions insufficientlyas a wiring board. The wiring board intermediate is, for example, one inwhich the electrical connection between the wiring layers isinsufficient. A more specific example of the wiring board intermediateis one in which a part of or all of a thermosetting resin is not curedcompletely, and the resin is contained as a matrix component in theelectrically insulating substrate that has through holes filled with aconductive paste. According to this method in which the electricallyinsulating substrate is superposed on the wiring board or the wiringboard intermediate, a multilayer wiring board in which two or morewiring layers are formed with the wiring transfer sheet of the presentinvention is efficiently produced by repeating steps (1) to (3).

[0058] In the case where the steps (1) to (3) are repeated using anelectrically insulating substrate containing an uncured thermosettingresin, in each step (2), heating and pressurization may be conductedunder the condition that the thermosetting resin is pre-cured so thatthe wiring layer of the wiring transfer sheet is temporarily adhered tothe electrically insulating substrate and an exposed area of a surfaceof the electrically insulating substrate on which the wiring layer isformed is roughened. The electrically insulating substrate istemporarily adhered to a wiring board or a wiring board intermediate. Inthe final step (2), heating and pressurization may be carried out underthe condition that the thermosetting resin contained in all electricallyinsulating substrates is post-cured. Pre-curing of a thermosetting resincontained in an electrically insulating substrate means that thethermosetting resin which is in a state in which the resin constitutesthe electrically insulating substrate (for example, a semi-cured state)is further cured but not cured completely. The pre-cured thermosettingresin can be further cured by heating and pressurization. Post-curing ofa thermosetting resin contained in an electrically insulating substratemeans that the thermosetting resin is cured so as to be in a state inwhich the resin cannot be further cured or a state close to this state.Therefore, pre-curing is carried out using a temperature and a pressurewhich are lower than those used in post-curing. A thermosetting resin ispre-cured or post-cured via a tacky state. Therefore, when step (2) iscarried out under the condition that the thermosetting resin ispre-cured or post-cured, the wiring layer is adhered to the electricallyinsulating substrate. Further, in the case where the electricallyinsulating substrate is superposed on a wiring board or a wiring boardintermediate, pre-curing of the thermosetting resin allows theelectrically insulating substrate to adhere to the wiring board or thewiring board intermediate. However, the extent of adhesion (adhesivestrength) obtained by pre-curing is lower than that obtained bypost-curing. Therefore, in this specification, the adhesion obtained bypre-curing of a thermosetting resin is referred to as a “temporaryadhesion.”

[0059] In a production method in which steps (1) to (3) are repeated,the thermosetting resin contained in all the electrically insulatingsubstrates is post-cured together in the final wiring transfer step. Thetechnique of post-curing together shortens a manufacturing timesignificantly. Further, according to this technique, it is possible toprevent the electrically insulating substrates which have been stackedfrom changing in dimension after every pro-curing of a newly stackedelectrically insulating substrate. Therefore, a finer wiring board ofhigher quality can be obtained. Alternatively, in every step (2), (wheneach of the steps (1) to (3) is carried out only once, in the step (2)carried out only once), heating and pressurization may be conductedunder the condition that the thermosetting resin contained in theelectrically insulating substrate is pre-cured. In that case, a wiringboard intermediate is obtained. Such an intermediate can be used, forexample, for producing a wiring board in which a component is disposedin an electrically insulating substrate, as mentioned below.

[0060] In the method for producing a multilayer wiring board byrepeating steps (1) to (3), electrically insulating substrates arepreferably superposed on both surfaces of the wiring board or the wiringboard intermediate in step (1). Such superposition is preferablyconducted when the temporary adhesion of the electrically insulatingsubstrates is carried out in sequence by pre-curing the thermosettingresin contained in the electrically insulating substrates followed bypost-curing the thermosetting resin together in the final wiringtransfer step. When the electrically insulating substrate is temporarilyadhered to one surface of the wiring board, the thermosetting resincontained in the electrically insulating substrates which have beensuperposed is further cured gradually by heat applied during everytemporary adhesion. As a result, displacement of the wiring layer and/orwarpage of the wiring board occur due to hardening shrinkage of theelectrically insulating substrate, which results in failure to obtain adesired wiring board. Such trouble is reduced or eliminated by disposingtwo electrically insulating substrates above and below the wiring boardor the wiring board intermediate followed by temporarily adhering themto the wiring board or the wiring board intermediate.

[0061] The second method for producing a wiring board of the presentinvention includes superposing an electrically insulating substrate on asurface of a wiring transfer sheet of the present invention whichsurface has a wiring layer. (2) Through holes are formed to expose thewiring layer of the wiring transfer sheet. (3) The through holes arefilled with a conductive paste, and (4) the wiring transfer sheet issuperposed on a wiring board or a wiring board intermediate through theelectrically insulating substrate. (5) A layered body which consists ofthe wiring transfer sheet, the electrically insulating substrate, andthe wiring board or the wiring board intermediate is heated andpressurized, so that the wiring layer of the wiring transfer sheetadheres to the electrically insulating substrate, and an exposed area ofa surface of the electrically insulating substrate on which surface thewiring layer is formed is roughened, while the electrically insulatingsubstrate adheres to the wiring board or the wiring board intermediate.(6) The carrier base of the wiring transfer sheet is removed. In thisproduction method, by using a wiring transfer sheet in which an exposedsurface of the carrier base has a plurality of concavities, convexitiescomplementary to the concavities are formed on an exposed area of asurface of the electrically insulating substrate.

[0062] This method corresponds to a method for obtaining a multilayerwiring board, in which another electrically insulating substrate issuperposed on a wiring board or a wiring board intermediate on which awiring layer has been formed, and then a wiring layer is formed on theelectrically insulating substrate. In this production method, a wiringtransfer sheet is superposed (that is, bonded) to an electricallyinsulating substrate, and then the electrically insulating substrate issuperposed on the wiring board or the wiring board intermediate.Therefore, according to this production method, the productivity of thewiring board can be improved. Further, according to this productionmethod, the alignment accuracy is improved since positions where throughholes are to be formed are adjusted by recognizing a position of awiring pattern formed on the wiring transfer sheet. Therefore, thethrough holes can be formed on a finer wiring. As a result, a wiringpattern of a higher density can be formed with a higher accuracy. Inthis production method, repeating the steps (1) to (6) makes it possibleto produce a multilayer wiring board efficiently by forming wiringlayers with wiring transfer sheets of the present invention.

[0063] In the second production method, like the first productionmethod, an electrically insulating substrate which contains an uncuredthermosetting resin is used as the electrically insulating substrate. Ineach step (5), heating and pressurization may be conducted under thecondition that the thermosetting resin is pre-cured so that the wiringlayer of the wiring transfer sheet is temporarily adhered to theelectrically insulating substrate and an exposed area of a surface ofthe electrically insulating substrate on which the wiring layer isformed is roughened, and the electrically insulating substrate istemporarily adhered to a wiring board or a wiring board intermediate. Inthe final step (5), heating and pressurization may be carried out underthe condition that the thermosetting resin contained in all electricallyinsulating substrates is post-cured. That is, also in the secondproduction method, the thermosetting resin contained in eachelectrically insulating substrate can be post-cured together in the lastwiring transfer step. The effect given by this operation is as describedin connection with the first production method. Alternatively, in everystep (5), (when each of the steps (1) to (6) is carried out only once,the step (5) is carried out only once), heating and pressurization maybe conducted under the condition that the thermosetting resin containedin the electrically insulating substrate is pre-cured. In that case, awiring board intermediate is obtained. Such an intermediate can be used,for example, for producing a wiring board wherein a component isdisposed in an electrically insulating substrate, as mentioned below.

[0064] In the method for producing a multilayer wiring board byrepeating the steps (1) to (6), wiring transfer sheets on which theelectrically insulating substrates are superposed are preferablysuperposed on both surfaces of the wiring board or the wiring boardintermediate in step (4). Such a superposition is preferably conductedwhen the temporary adhesion of the electrically insulating substratesare carried out in order by pre-curing the thermosetting resin containedin the electrically insulating substrates followed by post-curing thethermosetting resin together in the final wiring transfer step. Theeffect given by this superposition is as described above in connectionwith the first production method.

[0065] The present invention also provides a method for producing awiring board with a component disposed in an electrically insulatingsubstrate, which includes (A) superposing an electrically insulatingsubstrate having through holes filled with a conductive paste on awiring board or a wiring board intermediate. (B) A laminate is obtainedby heating and pressurizing a layered body which consists of theelectrically insulating substrate and the wiring board or the wiringboard intermediate so as to adhere the electrically insulating substrateto the wiring board or the wiring board intermediate. (C) A space isformed within the laminate in which space a component is to be placed.(D) The component is mounted on a wiring layer-formed surface of awiring transfer sheet of the present invention. (E) The wiring transfersheet is superposed on the laminate so as to dispose the component inthe space. (F) Heating and pressurization are performed so that thewiring layer of the wiring transfer sheet adheres to the electricallyinsulating substrate, and an exposed area of a surface of theelectrically insulating substrate on which surface the wiring layer isformed is roughened, while a void around the component is filled withthe resin contained in the laminate. (G) The carrier base of the wiringtransfer sheet is removed. This production method is characterized inthat a space in which the component is to be received is formed aftermaking the laminate dependant on the kind and size of the component.Further, this production method is characterized in that the componentis previously mounted on the wiring layer of the wiring transfer sheet,and then disposition of the component in the electrically insulatingsubstrate and transfer of the wiring layer are carried out at the sametime. Further, this production method is characterized in that the voidformed after disposing the component in the space is filled with theresin contained in the laminate (i.e. the resin contained in theelectrically insulating substrate), by forcing the resin to flow at thesame time as the transfer of the wiring layer. According to thisproduction method with these features, the component can be disposed inthe electrically insulating substrate with ease.

[0066] The wiring board or the wiring board intermediate employed in thestep (A) may be one produced according to the production method of thepresent invention. Preferably, the wiring board intermediate is used.The method for producing the wiring board intermediate is as describedin connection with the first and the second production methods forproducing the wiring board of the present invention.

[0067] The space formed in the step (D) may be a hole which penetratesthe laminate or a recess. In the step (F), the void which is formedafter disposing the component in the space is filled in by forcing thesurrounding resin which constitutes the laminate to flow into it. Theresin which constitutes the laminate is a resin contained in anelectrically insulating layer of the wiring board or the wiring boardintermediate used in the step (A), or a resin contained in theelectrically insulating substrate employed in the step (A). The resin isan uncured thermosetting resin or a thermoplastic resin. The viscosityof the resin is lowered by subjecting the resin to heating andpressurization treatment, resulting in flow of the resin.

[0068] In the case where the electrically insulating substratecontaining an uncured thermosetting resin is used in step (A), heatingand pressurization are preferably conducted under the condition that thethermosetting resin is pre-cured in the step (B). If the thermosettingresin is post-cured in the step (B), the thermosetting resin cannot flowin the step (F).

[0069] The void which is formed in the laminate after disposing thecomponent in the space is easily and securely filled when the void issurrounded by a resin which can flow by heating and pressurization.Therefore, in step (C), when a hole which penetrates the laminate in thethickness direction is formed as the space, a wiring board intermediatein which all electrically insulating layers contain an uncuredthermosetting resin is preferably used in step (A). When a recess isformed in the laminate as the space, a wiring board intermediate inwhich at least electrically insulating layer(s) where the recess is tobe positioned contains an uncured thermosetting resin is preferably usedin step (A). Alternatively, a wiring board or a wiring boardintermediate in which a part of or all of the electrically insulatingsubstrates contain a thermoplastic resin can be used. However, in somecase, the void around the component is fully filled when at least one ofthe electrically insulating substrates constituting the laminate containa resin which can flow. In such a case, for filling the void, itsuffices to use the electrically insulating substrate containing a resinwhich can flow by heating and pressurization, that is, an uncuredthermosetting resin or a thermoplastic resin, in step (A).

[0070] In step (A) of this production method, the wiring board or thewiring board intermediate can be produced by employing theabove-mentioned first method for producing the wiring board. That is,the following step (A′) is carried out in place of the step (A). Thestep (A′) is a step for obtaining a laminate, wherein a wiring board ora wiring board intermediate is produced by a method that includes (1)superposing a wiring transfer sheet of the present invention on anelectrically insulating substrate having through holes filled with aconductive paste. (2) Heating and pressurization are performed so as toadhere the wiring layer of the wiring transfer sheet to the electricallyinsulating substrate and to roughen an exposed area of a surface of theelectrically insulating substrate on which surface the wiring layer isformed. (3) The carrier base of the wiring transfer sheet is removed.Then, another electrically insulating substrate having through holesfilled with a conductive paste is disposed on the thus produced wiringboard or the wiring board intermediate. When the electrically insulatingsubstrate used in the step (1) contains an uncured thermosetting resin,and heating and pressurization are conducted under the condition thatthe thermosetting resin contained in the electrically insulatingsubstrate is pre-cured in step (2), a wiring board intermediate isobtained. When such a wiring board intermediate is produced in the step(A′), heating and pressurization are preferably carried out under thecondition that the thermosetting resin is post-cured in all electricallyinsulating substrates, in step (E).

[0071] Further, the other electrically insulating substrate which issuperposed on the wiring board or the wiring board intermediate producedin the step (A′) may be one containing an uncured thermosetting resin.Such an electrically insulating substrate may be disposed on a wiringboard intermediate in which electrically insulating layer(s) contain anuncured thermosetting resin. In that case, it is preferable that thekind of the thermosetting resin contained in this other electricallyinsulating substrate is the same as that contained in the wiring boardintermediate.

[0072] In the step (A′), the step (1) may further include superposingthe electrically insulating substrate on which the wiring transfer sheetis superposed, on the surface of a wiring board or a wiring boardintermediate which has been previously produced. The step (2) mayfurther include adhering the electrically insulating substrate to thesurface of the wiring board or the wiring board intermediate. In thatcase, in the step (A′), a multilayer wiring board is obtained. Thewiring board or the wiring board intermediate which has been producedpreviously may be produced according to the production method of thepresent invention.

[0073] Furthermore, by carrying out the steps (1) and (2) in this mannerand repeating the steps (1) to (3), a multilayer wiring board can bemade depending on the size and kind of component to be disposed. Whenrepeating the steps (1) to (3), the electrically insulating substratecontaining an uncured thermosetting resin is preferably used in therepeated steps (1), and heating and pressurization are conducted underthe condition that the thermosetting resin is pre-cured in the repeatedsteps (2), and the uncured thermosetting resin is together post-cured inthe step (E).

[0074] According to the present invention, it is possible to make asurface of a wiring board a rough surface, while ensuring surfacecoplanarity which is required for high density mounting of asemiconductor bare chip or an electronic component. When the surface ofthe wiring board is a rough surface, the contact area between the wiringboard and a resin stacked thereon is increased so that the adhesionbetween them is improved. Further, according to the present invention, asurface of the wiring board can be made a rough surface having fineconvexities. When a resin is stacked on a wiring board having such arough surface, the convexities provide an anchoring effect, whichimproves the adhesion between the wiring board and the resin.

BRIEF DESCRIPTION OF THE DRAWINGS

[0075] A more complete appreciation of the invention and many of theattendant advantages thereof will become readily apparent with referenceto the following detailed description, particularly when considered inconjunction with the accompanying drawings, in which:

[0076]FIG. 1(a) shows a schematic cross-sectional view of a wiringtransfer sheet of Embodiment 1 of the present invention, and FIGS. 1(b)and 1(c) show enlarged cross-sectional views of Areas B and A in thewiring transfer sheet shown in FIG. 1(a) respectively, and FIG. 1(d)shows a schematic cross-sectional view of a wiring board wherein awiring layer is transferred with the wiring transfer sheet shown in FIG.1(a), and FIGS. 1(e) and 1(f) show enlarged cross-sectional views ofAreas D and C in the wiring board shown in FIG. 1(d), respectively;

[0077]FIG. 2 shows a schematic cross-sectional view of a wiring transfersheet of Embodiment 2 of the present invention;

[0078]FIG. 3(a) shows a schematic cross-sectional view of a wiringtransfer sheet of Embodiment 3 of the present invention, and FIG. 3(b)shows an enlarged cross-sectional view of Area A in the wiring transfersheet shown in FIG. 3(a), and FIG. 3(c) shows a schematiccross-sectional view of a wiring board wherein a wiring layer istransferred with the wiring transfer sheet shown in FIG. 3(a), and FIG.3(d) shows an enlarged cross-sectional view of Area B in the wiringboard shown in FIG. 3(c);

[0079]FIG. 4(a) shows a schematic cross-sectional view of a wiringtransfer sheet of Embodiment 4 of the present invention, and FIG. 4(b)shows an enlarged cross-sectional view of Area A in the wiring transfersheet shown in FIG. 4(a), and FIG. 4(c) shows a schematiccross-sectional view of a wiring board wherein a wiring layer istransferred with the wiring transfer sheet shown in FIG. 4(a), and FIG.4(d) shows an enlarged cross-sectional view of Area B in the wiringboard shown in FIG. 4(c);

[0080] FIGS. 5(a) to 5(c) show schematic cross-sectional viewsillustrating the steps in an embodiment of a first method for producinga wiring transfer sheet of the present invention, and FIG. 5(d) shows anenlarged cross-sectional sectional view of Area A shown in FIG. 5(a),and FIG. 5(e) shows an enlarged cross-sectional sectional view of Area Bshown in FIG. 5(b);

[0081] FIGS. 6(a) to 6(c) show schematic cross-sectional viewsillustrating the steps in an embodiment of a second method for producinga wiring transfer sheet of the present invention, and FIG. 6(d) shows anenlarged cross-sectional view of Area A shown in FIG. 6(a), and FIG.6(e) shows an enlarged cross-sectional view of Area B shown in FIG.6(b), and FIG. 6(f) is an enlarged cross-sectional view of Area C shownin FIG. 6(c);

[0082] FIGS. 7(a) to 7(d) show schematic cross-sectional viewsillustrating the steps in an embodiment of a third method for producinga wiring transfer sheet of the present invention, and FIG. 7(e) shows anenlarged cross-sectional view of Area A shown in FIG. 7(a), and FIG.7(f) shows an enlarged cross-sectional view of Area B shown in FIG.7(d);

[0083] FIGS. 8(a) to 8(c) show schematic cross-sectional viewsillustrating the steps in an embodiment of a first method for producinga wiring board of the present invention, and FIG. 8(d) shows an enlargedcross-sectional view of Area A shown in FIG. 8(a), and FIGS. 8(e) and8(f) show enlarged cross-sectional views of Areas C and B shown in FIG.8(c), respectively;

[0084] FIGS. 9(a) to 9(g) show schematic cross-sectional viewsillustrating the steps in an embodiment of a second method for producinga wiring board of the present invention, and FIG. 9(h) shows an enlargedcross-sectional view of Area A shown in FIG. 9(a), and FIG. 9(i) showsan enlarged cross-sectional view of Area B shown in FIG. 9(g);

[0085] FIGS. 10(a) to 10(i) show schematic cross-sectional viewsillustrating the steps in another embodiment of the first method forproducing a wiring board of the present invention;

[0086] FIGS. 11(a) to 11(i) show schematic cross-sectional viewsillustrating the steps in an embodiment of a method for producing awiring board with a built-in component of the present invention;

[0087] FIGS. 12(a) to 12(c) show schematic cross-sectional viewsillustrating the steps in an embodiment of a method for producing awiring board with a built-in component which is a variation of theproduction method shown in FIG. 11;

[0088] FIGS. 13(a) to 13(c) show schematic cross-sectional viewsillustrating the steps in another embodiment of a method for producing awiring board with a built-in component which is a variation of theproduction method shown in FIG. 11;

[0089]FIG. 14(a) shows a schematic cross-sectional view illustrating thedepth of a concavity and a diameter on a surface of a carrier base ofthe concavity of a wiring transfer sheet of the present invention, andFIG. 14(b) shows a top view illustrating a diameter on a surface of acarrier base of the concavity, and FIG. 14(c) shows a schematicsectional view illustrating a convexity which is formed by the concavityshown in FIG. 14(a);

[0090] FIGS. 15(a) to 15(c) show embodiments of concavities of a wiringtransfer sheet of the present invention; and

[0091] FIGS. 16(a) to 16(c) show cross-sectional views illustrating thesteps in a method for producing a wiring board with a conventionalwiring transfer sheet, and FIG. 16(d) shows an enlarged cross-sectionalview of Area A shown in FIG. 16(a), and FIGS. 16(e) and 16(f) showenlarged cross-sectional views of Areas B and C shown in FIG. 14(c),respectively.

DETAILED DESCRIPTION OF THE INVENTION

[0092] In the following, embodiments of wiring transfer sheets of thepresent invention are described.

[0093] The wiring transfer sheet of the present invention is a sheetwhich includes a carrier base and a wiring layer. The carrier base ispreferably made from a material which is not compatible with anelectrically insulating substrate which is an object to which the wiringlayer is to be transferred, by heating and pressurizing a layered bodywhich consists of the wiring transfer sheet and the object upontransferring the wiring layer. The material for the carrier base isselected from an organic resin and a metal, depending on the material ofthe electrically insulating substrate. When the electrically insulatingsubstrate contains an epoxy resin, a polyimide resin, a cyanate resin, apolyphenylene ether (PPE) resin, or a polytetrafluoroethylene resin, thecarrier base is preferably made from a material selected from polyimide,a fluorine-containing resin, and a heat resistant epoxy resin. Further,the carrier base is preferably made from a material which is peeled offfrom the wiring layer in a step of removing the carrier base. From thisviewpoint, the carrier base is preferably made of a polyimide resin or afluorine-containing resin.

[0094] When the carrier base is made of a thermosetting resin, it isnecessary to take care of the compatibility between the resinconstituting the carrier base and a resin constituting the electricallyinsulating substrate. For example, when the carrier base is made of anepoxy resin and the electrically insulating substrate contains an epoxyresin, the viscosity of the epoxy resin which is not cured completely inthe carrier base reduces during the step of transferring the wiringlayer, and then mixes with the epoxy resin in the electricallyinsulating substrate, resulting in a failure to form convexitiescomplementary to concavities formed on the carrier base, on theelectrically insulating substrate. When the carrier base is made of athermoplastic resin and the step of transferring the wiring layer isconducted under the condition that the resin is softened, the sameproblem is caused. Therefore, when using a thermoplastic resin sheet asthe carrier base, the sheet is required to have heat resistance.

[0095] The thickness of the carrier base is selected depending on itsmaterial. Generally, it is preferably in the range of 10 to 100 μm. Whenthe carrier base is thin, this tends to cause problems in that handlingproperty thereof is bad, the strength thereof is decreased, and thecarrier base tends to be wrinkled. When the carrier base it too thick,there is a tendency that the carrier base is difficult to be peeled off.

[0096] The carrier base is preferably made from a material through whicha visible ray can pass. Such materials include a polyimide resin, afluorine-containing resin and a heat resistant epoxy resin. When thecarrier base is made from any one of these materials, its thickness ispreferably 100 μm or less for ensuring the transmission of the visibleray.

[0097] A surface of the carrier base on which the wiring layer is to beformed may be subjected to a releasing treatment. By subjecting thesurface to the releasing treatment, the carrier base is peeled offeasily from the object without damaging a rough surface, especiallyconvexities formed on the surface of the object after the wiring layerhas been transferred. The releasing treatment is conducted by coating asilicone resin to a thickness of between 0.01 and 1 μm on the surface ofthe carrier base on which the wiring layer is to be formed.

[0098] When the carrier base is made of a metal, it is preferable thatthe metals constituting the carrier base and the wiring layer are eachremoved selectively. Thereby, only the carrier base is removed byetching after the wiring layer has been transferred. The combinations ofthe carrier base/the wiring layer include aluminum/copper, andstainless/copper. When the metals constituting the carrier base and thewiring layer each cannot be removed selectively, an etching-stopperlayer is preferably provided between the carrier base and the wiringlayer. The material for the etching-stopper layer is selected dependingon the combination of the carrier base and the wiring, and the kind ofetchant. For example, when the combination of the carrier base/thewiring layer is copper/copper and the carrier base is removed by etchingwith a sulphuric acid/oxygenated water, the etching-stopper layer ispreferably made of titanium.

[0099] The carrier base may be a laminate comprising a plurality oflayers. In that case, the layer which has a surface on which the wiringlayer is to be formed (this layer is also referred to as a“wiring-forming layer”) may be a layer formed from a material which isnot compatible with the electrically insulating substrate. Suchmaterials have been exemplified above. When the carrier base is thelaminate, it is particularly preferable that the wiring-forming layer isformed from an organic resin such as a fluorine-containing resin. Thethickness of the wiring-forming layer is preferably in the range of 5 to60 μm.

[0100] The other layer(s) which are laminated on the wiring-forminglayer preferably include a layer which gives strength and a rigidity tothe wiring transfer sheet. This layer is also referred to as a“supporting layer.” The preferable supporting layer is specifically ametal foil having a thickness of between 30 and 100 μm (for example, analuminum foil, a copper foil or a stainless foil) or a resin film havinga thickness of between 50 and 200 μm (for example, a PET film or a PENfilm). More preferably, a copper foil is used. When the wiring layer ismade of copper, the use of a copper foil as the supporting layerprevents the wiring transfer sheet from warping since the same materialis positioned on both surface sides of the carrier base. Alternatively,the supporting layer may be a layer made of a thermally foaming resin(for example, REVALPHA (trade name) available from NITTO DENKOCORPORATION). The supporting layer is made of two or more layers.

[0101] As described above, the carrier base may be a sheet made of anorganic resin. However, dimensional change of the organic resin sheettends to be caused by heating, and it may be caused at the time offorming a wiring layer into a desired pattern by etching. It isdesirable that the dimensional change of the carrier base is avoidedbecause the dimensional change causes displacement of wire. Therefore,when the organic resin sheet is used as the carrier base, the carrierbase is preferably made as a two-layer structure by superposing thesupporting layer such as a metal foil on a surface which is opposite tothe surface on which the wiring layer is to be formed, so that thedimensional change lessens or does not occur.

[0102] The supporting layer is removed together with the wiring-forminglayer after the wiring layer has been transferred. When the supportinglayer is made of a metal, etching is a simple method for removing thesupporting layer. When the supporting layer is made of a thermallyfoaming resin, it is easily removed by heating upon transferring thewiring layer. When the supporting layer is made of a material whose heatresistance is low (for example, a resin), it is necessary to remove thesupporting layer before transferring the wiring layer. In that case, theremoval of the supporting layer is carried out by, for example, breakingor removing the portion where the supporting layer and the wiring layerare fixed to each other (for example, a bonded point formed by using anadhesive agent).

[0103] When the carrier base is made of a plurality of layers, thelayers may be fixed to each other over the entire interface between thelayers, or at a part of the entire interface (for example, at theperiphery). When one of the layers has adhesiveness, the fixationbetween the layers may be conducted by using the adhesiveness of thelayer. Alternatively, the fixation may be conducted by using an adhesiveagent.

[0104] The wiring layer of the wiring transfer sheet is made from aconductive material which is generally used as a material for a wiringlayer of a wiring board. Specifically, the wiring layer is made ofcopper, a copper alloy, or silver. Further, the wiring layer has apredetermined pattern depending on a wiring pattern which is to beformed on a wiring board. In the wiring transfer sheet, the wiring layeris buried in the carrier base so that the wiring layer protrudes from(or is buried in) the electrically insulating substrate as desired in awiring board after the wiring layer has been transferred to the board.For example, the wiring layer is buried in the carrier base so that thesurface thereof is flush with the surface of the carrier base. In thatcase, almost the entire thickness of the wiring layer which is formed onthe electrically insulating substrate protrudes from the electricallyinsulating substrate.

[0105] A surface of the wiring layer which does not contact the carrierbase is preferably a rough surface. It is particularly preferable thatthe rough surface has a plurality of convexities. The reason for this isas described above. As described below, the convexities formed on thesurface of the wiring layer are formed by depositing metal particles onthe originally flat surface of a metal foil (for example, a copper foil)through electrolytic plating under the condition selected appropriately.In the convexity, of the sections which are parallel to the surface ofthe wiring layer, the section having the maximum area preferably has adiameter of between 1 and 10 μm. Further, the convexity has a height ofbetween 0.5 and 5 μm. Here, the height of the convexity is the shortestdistance between the basis and the top of the convexity. Morepreferably, the convexity has a shape which swells at the waist, such asa mushroom-shape, a bump-shape or a bud-shape, so that it can provide agreater anchoring effect. As described above, the convexity of such ashape is formed by depositing fine metal particles so that they areflocculated and/or piled up through electrolytic plating under theappropriately-selected condition.

[0106] In the wiring transfer sheet of the present invention, at aposition where no wire is formed as a result of patterning, a surface ofthe carrier base is exposed. The exposed surface of the carrier base isa rough surface, and preferably has a plurality of fine concavities. Asdescribed above, the concavities serve to form convexities whose shapesare complementary to the concavities. As described above with referenceto FIG. 15, the concavity preferably has a shape wherein the area of thesection which is perpendicular to the thickness direction of the carrierbase (that is, a section along the direction parallel to the surface ofthe carrier base) is greatest at an intermediate position between thesurface and the bottom of the carrier base. The shapes of theconcavities are not limited to those shown in FIG. 15 and may be otherones. The preferable proportion of the concavities on the exposedsurface of the carrier base and the preferable size of each concavityare as described above. The concavities do not necessarily have the samesize and the same shape in one wiring transfer sheet. Generally,concavities which differ in size and/or shape exist in one wiringtransfer sheet. The concavities are preferably distributed uniformly.

[0107] As described above, a junction layer may be interposed betweenthe carrier base and the wiring layer. The junction layer is made of ametal which is different from the wiring layer, or an oxide of metal.Specifically, the junction layer is made from a material selected fromCr, Zn, Ni, and the oxides thereof. The thickness of the junction layeris preferably in the range of 0.01 to 1 μm. When the junction layer istoo thick, the junction layer which remains on the surface of the wiringlayer after the wiring layer has been transferred may adversely affectthe electrical connection between the wiring layers. Since an organicresin is difficult to adhere to copper, the junction layer is preferablyprovided when the carrier base is made of an organic resin and thewiring layer is made of copper.

[0108] Next, an electrically insulating substrate for a wiring board isdescribed. The electrically insulating substrate is the object to whichthe wiring layer of the wiring transfer sheet of the present inventionis to be transferred. Any one of the electrically insulating substrateswhich are conventionally used as electrically insulating substrates fora wiring board may be used. A porous substrate which can be compressedor a three-layer structure substrate wherein adhesive layers are formedon both surfaces of a core film is generally used as the electricallyinsulating substrate. Specifically, a resin impregnated fibrous sheetcan be used as the electrically insulating substrate, which is obtainedby impregnating a non-woven fabric, a woven fabric or a paper with athermosetting resin followed by semi-curing the resin. Morespecifically, a composite substrate in which a sheet of glass fibers oraramid fibers is impregnated with an epoxy resin or a bismaleimidetriazine (BT) resin can be used. Since these composites are poroussubstrates which can be compressed, when the electrically insulatingsubstrate has through holes filled with a conductive paste as describedbelow, the composites allow the conductive paste to be subjected to acompression effect. Alternatively, a substrate containing athermoplastic resin such as a polyetheretherketone (PEEK) resin, apolyetherimide resin, a PTFE resin or a liquid crystal polymer can beused as the electrically insulating substrate. The surface of theelectrically insulating substrate on which the wiring layer is to beformed has little swell and coplanarity which is required for mounting asemiconductor bare chip or an electronic component at a higher density.

[0109] As described above, the electrically insulating substratepreferably has through holes that are formed in a thickness directionand are filled with a conductive paste. The size and the position ofeach through hole are selected so that the wiring layers are connectedas desired. The through holes are formed by a conventional method.Specifically, the through holes are formed through a laser process usinga carbon dioxide laser, an eximer laser or a YAG laser. Any one of theconductive pastes which are used in the production process of theabove-mentioned All Layers IVH structure resin multilayer wiring board,may be used. The conductive paste is specifically a paste which is madeof powder of Cu, Ag, Pd, or an alloy thereof, and a resin such as anepoxy resin or a phenol resin. The resin component is in a state ofcured in an end product. Further, the conductive paste ensures theelectrical connection between the wiring layers by being densified inthe wiring board by being subjected to a compression effect.

[0110] Further, in the wiring board of the present invention, acomponent connected with the wiring layer is disposed in an electricallyinsulating substrate. The component is, for example, a passive componentsuch as LCR, a SAW filter, or a TCXO. The component may be disposed inone electrically insulating layer, or may stretch from one electricallyinsulating layer to another one or two electrically insulating layersdepending on its size.

[0111] Hereinafter, more specific embodiments of the wiring transfersheets and the wiring boards of the present invention are described withreference to the drawings.

[0112] Embodiment 1

[0113] In FIG. 1, a wiring transfer sheet of Embodiment 1 of the presentinvention and a wiring board which is produced using the wiring transfersheet are schematically shown in sectional views. FIG. 1(a) shows awiring transfer sheet 100 wherein a wiring layer 102 is formed in apredetermined pattern on a surface of a carrier base 101. FIG. 1(b)shows an enlarged view of Area B which is an exposed area of a surfaceof the carrier base on which the wiring layer is formed. FIG. 1(c) showsan enlarged view of Area A in the vicinity of the wiring layer of thewiring transfer sheet. FIG. 1(d) shows a wiring board 100 which isobtained by transferring a wiring layer 103 to an electricallyinsulating substrate 104 using the wiring transfer sheet shown in FIG.1(a). FIG. 1(e) shows an enlarged view of Area D that is an exposedsurface of the electrically insulating substrate, which is a part of asurface of the wiring board which surface has the wiring layer. FIG.1(f) shows an enlarged view in the vicinity of the wiring layer of thewiring board.

[0114] As shown in FIG. 1(c), the wiring layer 102 is formed on asurface of the carrier base 101 in a state in which the wiring layer 102enters concavities which are formed on the surface of the carrier base101. That is, the interface between the carrier base 101 and the wiringlayer 102 is uneven. Therefore, the contact area between the carrierbase 101 and the wiring layer 102 is larger compared with a case inwhich the interface between them is flat. For this reason, they adhereto each other so that the wiring layer is well carried on the carrierbase without an adhesive layer therebetween, until the wiring istransferred to an object. Nonuse of an adhesive agent is convenientbecause the adhesive agent does not remain on a surface of the wiringlayer after the wiring layer has been transferred. The method forobtaining such an interface is described below. As shown in FIG. 1, inthis wiring transfer sheet 100, the exposed surface of the wiring layer102 is flat.

[0115] The wiring board is obtained by superposing the wiring transfersheet on an electrically insulating substrate for a wiring board withthe wiring layer in contact with a surface of the electricallyinsulating substrate followed by heating and pressurization so as totransfer the wiring layer to the electrically insulating substrate. Thestructure of the wiring layer thus obtained is as shown FIG. 1(d). Inthis wiring board 110, the wiring layer 103 is entirely buried in theelectrically insulating substrate 104, and an exposed surface of thewiring layer 103 is flush with an exposed surface of the electricallyinsulating substrate 104. This is because the wiring layer 102 protrudesin the wiring transfer sheet 100 shown in FIG. 1(a). During the step oftransferring the wiring layer, pressure is applied so that the wiringlayer is brought into contact with the object without a gaptherebetween, whereby the protruding wiring layer is buried in theelectrically insulating substrate.

[0116] As shown in FIG. 1(e), in the wiring board 110, convexities 130complementary to concavities 120 of the wiring transfer sheet 100 areformed on an exposed surface of the electrically insulating substrate104. A material of the electrically insulating substrate flows into theconcavities while the transfer of the wiring layer is carried out, whichresults in forming these concavities. Each of the convexities is abump-shaped, a bud-shaped, or a mushroom shaped one. The convexities ofthese shape provide a greater anchoring effect than the convexitieswhose sectional areas parallel to the surface of the wiring board areuniform (for example, a column-shape convexity) when a resin islaminated thereon, resulting in improved adhesion between the wiringboard and the laminated material.

[0117] Further, as shown in FIG. 1(f), this wiring board has fineconvexities on a surface of the wiring layer 103. This is because theinterface between the wiring layer 102 and the carrier base 103 isuneven in the wiring transfer sheet and the convexities of the wiringlayer 102 are exposed by peeling off the carrier base after the wiringlayer has been transferred. The convexities on the wiring layer 103, aswell as the convexities on the electrically insulating substrate 104,contribute to the increase of the contact area between the wiring layerand the stacked resin, and provide an anchoring effect. Therefore, thiswiring board in which the convexities exist on not only the surface ofthe electrically insulating substrate but also the surface of the wiringlayer, strongly adheres to the resin stacked thereon.

[0118] (Embodiment 2)

[0119] In FIG. 2, a wiring transfer sheet of Embodiment 2 of the presentinvention is schematically shown in sectional view. In a wiring transfersheet 200 shown in FIG. 2, a carrier base 201 is formed of awiring-forming layer 240 and a supporting layer 250, and a wiring layer202 is formed on a surface of the wiring forming layer 240. In thiswiring transfer sheet 200, the concavities (not shown) are formed on anexposed surface of the wiring-forming layer. The materials suitable forconstituting the wiring-forming layer 240 and the supporting layer 250are as described above. More specifically, as a combination ofsupporting layer/wiring forming layer, a copper foil/afluorine-containing resin is exemplified.

[0120] (Embodiment 3)

[0121] In FIG. 3, a wiring transfer sheet of Embodiment 3 of the presentinvention and a wiring board which is produced using the wiring transfersheet are schematically shown in sectional views. FIG. 3(a) shows awiring transfer sheet 300 wherein a wiring layer 302 is buried in acarrier base 301. FIG. 3(b) shows an enlarged view of Area A in thevicinity of the wiring layer of the wiring transfer sheet. FIG. 3(c)shows a wiring board 310 which is obtained by transferring a wiringlayer 303 to an electrically insulating substrate 304 using the wiringtransfer sheet shown in FIG. 3(a). FIG. 3(d) shows an enlarged view ofArea B in the vicinity of the wiring layer of the wiring board.

[0122] As shown in FIG. 3(b), almost the entire thickness of the wiringlayer 302 is buried in the carrier base 301 so that a surface of thewiring layer 302 is substantially flush with a surface of the carrierbase 301. Such a wiring transfer sheet is produced by forming the wiringlayer in a predetermined pattern followed by thermally pressing thewiring layer into the carrier base. The wiring transfer sheet 300 is thesame as the wiring transfer sheet shown in FIG. 1(a) except that thewiring layer 302 is buried in the carrier base 301. The shape ofconcavities and the interface between the carrier base 301 and thewiring layer 302 are as described above with reference to FIG. 1.

[0123] A wiring board 310 as shown in FIG. 3(c) is obtained bytransferring the wiring layer of this wiring transfer sheet to a surfaceof an electrically insulating substrate through heating andpressurization. As shown in FIG. 3(d), in the wiring board 310, thetransferred wiring layer 303 protrudes from the surface of theelectrically insulating substrate 304. When a semiconductor bare chip orthe like is mounted on the surface of the wiring layer 303, the gapbetween the semiconductor bare chip and the surface of the wiring boardis larger compared with the case where the bare chip is mounted on thewiring board shown in Fig. (d). As described above, the larger the gapis, the easier a sealing resin for protecting the mounting is injected.As described above with reference to FIG. 1(f), the surface of thewiring layer 303 has convexities.

[0124] (Embodiment 4)

[0125] In FIG. 4, a wiring transfer sheet of another embodiment of thepresent invention and a wiring board which is produced using the wiringtransfer sheet are schematically shown in sectional views. FIG. 4(a)shows a wiring transfer sheet 400 wherein a wiring layer 402 is formedon a surface of a carrier base 401. FIG. 4(b) shows an enlarged view ofArea A in the vicinity of the wiring layer of the wiring transfer sheet.FIG. 4(c) shows a wiring board 410 which is obtained by transferring awiring layer 403 to an electrically insulating substrate 404. FIG. 4(d)shows an enlarged view of Area B in the vicinity of the wiring layer ofthe wiring board.

[0126] As shown in FIG. 4(b), in the wiring transfer sheet 400, theinterface between the wiring layer 402 and the carrier base 401 isuneven, while the exposed surface of the wiring layer 402 hasconvexities. The remaining construction of the wiring transfer sheet 400is as described with reference to FIG. 1.

[0127] The wiring board 410 of the structure as shown in FIG. 4(c) isobtained by transferring the wiring layer of this wiring transfer sheetto a surface of an electrically insulating substrate though heating andpressurization. As shown in FIG. 4(d), in the wiring board 410, theconvexities on the exposed surface of the wiring layer 402 of the wiringtransfer sheet 400 ensure favorable adhesion between the wiring layer403 and the electrically insulating substrate 404.

[0128] Next, a method for producing a wiring transfer sheet of thepresent invention is described. As described above, there are first,second and third production methods for producing the wiring transfersheet of the present invention. In the first production method, a wiringmaterial sheet which has a rough surface is used, and this sheet ispressed against a carrier base so as to make a surface of the carriersheet another rough surface complementary to the rough surface of thewiring material sheet. Then a wiring layer having a predeterminedpattern is formed by patterning the wiring material sheet.

[0129] The wiring material sheet whose surface is a rough surface ispreferably a sheet whose surface has a plurality of convexities. As oneembodiment of the first production method, an embodiment in which such asheet is used, is described thereinafter.

[0130] The wiring material sheet is, for example, a metal foil. Themetal foil is preferably formed from a metal exemplified above as ametal which preferably constitutes the wiring layer. The metaloriginally has a flat surface. In order to make this flat surface arough surface, it is preferable that metal particles are deposited on asurface of the metal foil through electrolytic plating so as to form aplurality of convexities. As described above, each convexity formed byelectrolytic plating has a structure in which the metal particlesdeposited through electrolytic plating are flocculated and/or piled up.Electrolytic plating is preferably employed as a method for forming theconvexities from the viewpoint of productivity.

[0131] The size of the metal particles deposited through electrolyticplating (this particle is merely referred to as a “deposited particle”)is selected so that the shape of the rough surface (for example, thesize of the concavity) which is to be formed on the surface of thecarrier base is a desired one. When the size of the deposited particleis small, the concavity formed on the surface of the carrier base issmall, so that the size of the convexity formed on the electricallyinsulating substrate of the wiring board becomes small. As a result, asufficient anchoring effect is not obtained when a resin is stacked onthe surface of the wiring board. When the size of the deposited particleis large, the number of convexities which exist between the wiring layerand the carrier base is small when the wiring layer of fine width (forexample, 20 μm or less) is formed by patterning the metal foil. As aresult, the adhesion between the wiring layer and the carrier baseprovided by an anchoring effect of the convexities becomes insufficient,which causes the wiring layer to exfoliate from the carrier base.Specifically, the deposited particle is preferably a round shape havinga diameter in the range of 0.1 μm to 4 μm. The convexity preferably hasa form wherein a plurality of the deposited particles of this size areflocculated and/or piled up, and as a whole preferably has theabove-mentioned size (that is, a diameter of between 1 and 10 μm at thesection whose area is largest, and a height of between 0.5 and 5 μm).However, the convexity does not necessarily need to be formed of aplurality of the deposited particles, and may be formed of one depositedparticle.

[0132] The wiring material layer which has a plurality of convexities issuperposed on a carrier base with the convexities in contact with asurface of the carrier base, and then is pressed against the carrierbase so as to bury the convexities in the carrier base and to beintegrated with the carried base. Therefore, in this production method,it is necessary to use a base which is made from a material into whichthe convexity on the wiring material sheet can be buried, as the carrierbase. Specifically, the carrier base needs to be a sheet of an organicresin, or a laminate wherein a wiring forming layer is made of anorganic resin. In that case, an organic resin which is suitable forconstituting the carrier base is a heat resistant resin such as afluorine-containing resin as described above.

[0133] When the convexities on the wiring material sheet are buried inthe carrier base, the wiring material sheet and the carrier base areintegrated by an anchoring effect of the convexities. In order toimprove the adhesion between them, a junction layer may be interposedbetween the wiring material layer and the carrier base. The materialsuitable for the junction layer is as described above. The junctionlayer is formed by, for example, plating the surface of the wiringmaterial sheet on which the convexities are formed. For example, when aCr or a Ni layer is formed by plating, it passivates in the atmosphericair which results in improved adhesion. The junction layer may be formedon a surface of the carrier base.

[0134] Before superposing the wiring material sheet, a surface of thecarrier base is subjected to a releasing treatment. The purpose andmethod of the releasing treatment are described in relation to thecarrier base, the description thereof being omitted here. The releasingtreatment is preferably conducted when the carrier base is made of anepoxy resin. The releasing treatment is not required when the carrierbase is made from a material which exhibits an excellent release-abilityas to the electrically insulating substrate itself (e.g. afluorine-containing resin).

[0135] The integration of the wiring material sheet with the carrierbase is carried out by superposing the wiring material sheet on thecarrier base followed by heating and pressurization so as to make closecontact therebetween. The heating and pressurization are carried outunder the condition that the carrier base is softened so as to deformdue to the convexities on the wiring material sheet, and the carrierbase does not deteriorate. When the carrier base is made of athermoplastic resin, the heating and pressurization are conducted underthe condition that the carrier base is softened. When the carrier baseis made of a thermosetting resin, the thermosetting resin is in anuncured or a semi-cured state in the carrier base before heating andpressurization, and the heating and pressurization are carried out sothat the thermosetting resin is softened and the viscosity of the resinis reduced. Thus, concavities complementary to the convexities areformed, and then the resin is cured. Further, the heating andpressurization are carried out in an inert gas atmosphere or a vacuumatmosphere, if necessary, so that the wiring material sheet is notoxidized.

[0136] After integrating the wiring material sheet with the carrierbase, a wiring layer having a predetermined wiring pattern is formed byetching the wiring material. Thereby, the wiring transfer sheet isobtained. Etching is carried out through a conventional technique withan appropriate etchant selected depending on the wiring material. Withina region from which the wiring material is removed by etching, thesurface of the carrier base is exposed. On the exposed surface of thecarrier base, the concavities exist. Further, in the wiring transfersheet produced by this production method, the interface between thecarrier base and the wiring layer is a structure wherein the wiringlayer enters the concavities of the carrier base. This structure resultsfrom the convexities of the wiring material sheet being buried into thecarrier base.

[0137] In FIGS. 5(a) to 5(c), the major steps of the first method forproducing a wiring transfer sheet of the present invention are shown. InFIG. 5(a), a carrier base 501 and a wiring material sheet 502 are shown,respectively. In FIG. 5(d), an enlarged view of Area A of a surface ofwiring material sheet. As shown in FIG. 5(d), on the entire surface ofthe wiring material sheet, bump-shaped, mushroom-shaped, or bud-shapedconcavities 530 are formed. The junction layer (not shown) may bepreviously formed on the surface of the carrier base 501 or the wiringmaterial sheet 502. Further, the surface of the carrier base 501 may bepreviously subjected to a releasing treatment.

[0138]FIG. 5(b) shows a step of superposing the carrier base 501 on thewiring material sheet 502 followed by heating and pressurization so thatthe carrier base adheres to the wiring material, and thereby theconvexities are buried in the carrier base. By burying the convexities,concavities complementary to the convexities are formed on a surface ofthe carrier base.

[0139]FIG. 5(c) shows a step of etching the wiring material sheet 502 soas to form a wiring layer 503 in a predetermined wiring pattern. FIG.5(e) shows an enlarged view of Area B in the vicinity of the wiringlayer. As shown in FIG. 5(e), concavities 520 are formed on an exposedsurface of the carrier base 501, which results from removal of thewiring material sheet, and the interface between the carrier base 501and the wiring layer 503 is uneven.

[0140] In the above, there is described an embodiment wherein the wiringmaterial sheet which has a plurality of convexities on its surface isused. The surface (rough surface) of the wiring material sheet is notlimited to one which has a plurality of convexities. For example, thesurface of the wiring material sheet may be a rough surface which has aplurality of concavities. Further, it is advantageous that the carrierbase 501 is a two-layer structure which has a sheet of an organic resinand a copper foil, in terms of dimensional stability and handlingproperty.

[0141] Next, the second method for producing a wiring transfer sheet ofthe present invention is described. In the second production method, awiring layer with a predetermined pattern is formed on a surface of acarrier base, and then the exposed surface of the carrier base is made arough surface by subjecting it to a roughening treatment. The rougheningtreatment is preferably carried out so that a plurality of concavitiesare formed. Thereinafter, as one embodiment of the second productionmethod, an embodiment in which the roughening treatment is carried outso that a plurality of concavities are formed, is described.

[0142] This production method is preferably employed when a carrier baseis made from a material which does not deform by heating andpressurization, such as a metal foil. This is because, when anothersheet (that is, the wiring material sheet) with convexities issuperposed on and integrated with such a carrier base according to thefirst production method, it is difficult to form concavitiescomplementary to the convexities on the carrier base. This productionmethod is preferably employed when the carrier base is an aluminum foil,a stainless foil, or the like.

[0143] In the case where the carrier base is a metal foil such as analuminum foil, the wiring layer is formed by depositing a wiringmaterial such as copper through electrolytic plating followed bypatterning. In that case, a surface of the metal foil is preferably flatso that a uniform layer is formed through electrolytic plating.

[0144] With some kinds of metal foils, it is difficult to depositdirectly on the surface of the metal foil by plating. In that case, thewiring material may be plated on a junction layer which has beenpreviously formed on the surface of the carrier base, whereby goodadhesion between the carrier base and the wiring layer can be ensured.For example, when the carrier base is an aluminum foil and the wiringlayer is made of copper, a zinc layer is preferably formed on thesurface of the aluminum foil as the junction layer through electrolyticplating. In that case, copper is deposited on the surface of the zinclayer through electrolytic plating.

[0145] The wiring material layer deposited on the surface of the carrierbase is patterned by etching so that the wiring layer with apredetermined pattern is formed. When both the carrier base and thewiring layer are made of metals, a combination of the carrier base andthe wiring layer is selected so that only the metal constituting thewiring layer is etched, or an etching rate of the metal constituting thecarrier base is lower than that of the metal constituting the wiringlayer. When the carrier base and the wiring layer is made of metals ofthe same kind, it is preferable that an interlayer is formed between thecarrier base and the wiring layer as an etching stopper layer, andtherefore the wiring layer is formed on the surface of the interlayer. Amaterial constituting the interlayer is optimally selected depending onthe combination of the carrier base and the wiring layer, and the kindof etchant. Generally, the material is selected from chromium, nickel,cobalt, titanium, and zinc. For example, when the combination of acarrier base of copper and a wiring layer of copper is employed and asulfuric acid-based etchant is used, the interlayer is preferably madeof aluminum, titanium, or chromium. When an aqueous solution of ferricchloride or cupric chloride is used as an etchant for this combination,the interlayer is preferably made of titanium or stainless. Theseinterlayers also serve as an etching stopper layer when the carrier baseis removed by etching after the wiring has been transferred to anelectrically insulating substrate. When the carrier base is a stainlessfoil or an aluminum foil and the wiring layer is made of copper, such aninterlayer is generally unnecessary.

[0146] After etching the wiring material, the surface of the carrierbase is exposed within an area from which the wiring material is removedby etching. The exposed surface of the carrier base is subjected to theroughening treatment so that a plurality of concavities are formed. As amethod of the roughening treatment, a dry-etching with a reactive gas, amachining with sandblast, and an electrolytic etching can be employed.When the carrier base is an aluminum foil, fine pit-shaped concavitiescan be formed by electrolytic etching with a hydrochloric acid-basedetchant. When carrying out the roughening treatment, an etching resistthat has been used for forming the wiring layer, is preferably left onthe wiring layer. The reason for this is that the wiring layer isprotected by the etching resist so that it is not damaged during theroughening treatment. In the case where the roughening treatment isconducted in this manner, the etching resist is removed after theroughening treatment.

[0147] FIGS. 6(a) to 6(c) show the major steps of the second method forproducing a wiring transfer sheet of the present invention. FIG. 6(a)shows the step of superposing a layer 602 of a wiring material on asurface of a carrier base 601 which is a metal foil. An enlarged view ofthe interface (Area A) in the composite 603 obtained in FIG. 6(a) isshown in FIG. 6(d). In the illustrated embodiment, the interface is flatsince the wiring material such as copper is laminated on the metal foilthrough electrolytic plating. The composite in which a layer of wiringmaterial is formed on a metal foil is commercially available. Forexample, a composite in which a copper layer is formed on a surface ofan aluminum foil is commercially available under the trade name “UTCcopper foil” from Mitsui Mining & Smelting Co., Ltd. In the productionmethod of the present invention, such a commercially available compositemay be used for carrying out the following steps.

[0148]FIG. 6(b) shows a step of forming a wiring layer 604 by patterningthe wiring material layer 602 through etching. As described above,etching is carried out so that only a part of the wiring material layer602 is removed. FIG. 6(e) shows an enlarged view of an exposed surfaceof the carrier base (Area B) after the step of FIG. 6(b) has beenconducted. As shown, at this stage, the exposed surface of the carrierbase 601 is flat.

[0149]FIG. 6(c) shows a step of subjecting the exposed surface of thecarrier base 601 to a roughening treatment after the step of FIG. 6(b)has been conducted. FIG. 6(f) shows an enlarged view of the exposedsurface of the carrier base (Area C) after the roughening treatment hasbeen conducted. As shown, a plurality of concavities 620 are formed onthe exposed surface of the carrier base. The roughening treatment isconducted so that a predetermined number of concavities withpredetermined shapes are obtained depending on the shapes and so on ofconvexities to be formed on an object, that is, an electricallyinsulating substrate.

[0150] This second method for producing a wiring transfer sheet isemployed not only when the carrier base is a metal foil, but also whenit is made of a resin. When the carrier base is a sheet of resin, alayer or a wiring material is formed on the carrier base by electrolessplating, a method in which electroless plating and electrolytic platingare combined, or vacuum film forming followed by etching the layer ofwiring material so as to form a wiring layer of a predetermined pattern.

[0151] In the above, the embodiment in which the roughening treatment iscarried out so that a plurality of concavities are formed, is described.The roughening treatment is not limited to one in which the concavitiesare formed on the exposed surface of the carrier base. For example, theroughening treatment may be conducted so that a plurality of convexitiesare formed on the exposed surface of the carrier base.

[0152] Next, the third method for producing a wiring transfer sheet ofthe present invention is described. In the third production method, asurface of a carrier base is made a rough surface, and then a metal isdeposited on the rough surface in a predetermined pattern by plating,whereby a wiring layer is formed. The surface of the carrier base ispreferably made a rough surface which has a plurality of concavities.Thereinafter, as one embodiment of the third production method, anembodiment in which a plurality of concavities are formed on a surfaceof a carrier base, and then a wiring layer is formed, is described.

[0153] The method for forming concavities on a surface of the carrierbase is as described in relation to the second production method. Whenthe carrier base is made of a resin, the concavities may be formed bypressing concavities into the carrier base using a roller or a metallicdie which has convexities or a metal foil which has convexities formedby electrolytic plating, or may be formed by machining. When the carrierbase is made of a supporting layer and a wiring-forming layer that ismade of a resin, the concavities may be formed in the same manner. Theconvexities formed on the roller, the metallic die or the likepreferably have shapes that are to be formed on the object. Theconvexities on the roller and so on are pressed (or transferred) so asto form the concavities on the carrier base, and other convexitiescomplementary to the concavities of the carrier base are formed on theobject. In other words, the shapes of the concavities on the roller andso on can control a surface shape of a wiring board.

[0154] Next, a photoresist is formed on the surface of the carrier basewhere the concavities are formed, and then it is subjected topatterning. For example, the photoresist is formed by laminating a dryfilm type material. The patterning is carried out so that openingsresulting from the patterning form a predetermined wiring pattern. Next,a metal is deposited in the openings through plating, whereby a wiringlayer is formed. When the carrier base is made of a metal, thedeposition of metal is preferably carried out by electrolytic platingfrom the viewpoint of productivity. When the carrier base is made of aresin, a metal can be deposited by electroless plating. The metaldeposited through plating is generally copper. Since the metal depositedthrough plating enters the concavities on the carrier base, theinterface between the carrier base and the wiring layer become uneven ina wiring transfer sheet obtained by this method. Next, the wiringpattern in the predetermined pattern is formed by removing thephotoresist, whereby the wiring transfer sheet is obtained.

[0155] FIGS. 7(a) to 7(d) show major steps of the third method forproducing a wiring transfer sheet of the present invention. FIG. 7(a)shows a step of forming concavities 720 on a surface of a carrier base701. FIG. 7(e) shows an enlarged view of the surface of the carrier base701 (Area A). As shown, in the carrier base 701, a number ofbump-shaped, mushroom-shaped or bud-shaped concavities are formed.

[0156]FIG. 7(b) shows the step of forming a photoresist 702 on thesurface of the carrier base 701 and subjecting the photoresist 702 topatterning. By patterning, openings 740 in which a wiring layer is to beformed are formed in the photoresist 702. FIG. 7(c) shows the step ofdepositing the wiring material 703 in the openings 740 in thephotoresist 702 by plating. FIG. 7(d) shows the step of removing thephotoresist so as to form a wiring layer 703. FIG. 7(e) shows anenlarged view of Area B in the vicinity of the wiring layer in thewiring transfer sheet obtained by carrying out the step of FIG. 7(d). Asshown, the concavities 720 exist on the exposed surface of the carrierbase. The interface between the carrier base 701 and the wiring layer703 is uneven so that the carrier base and the wiring layer closelyadhere to each other. Therefore, in the wiring transfer sheet of thisconstruction, the adhesion between the carrier base and the wiring layeris good.

[0157] In the above, the embodiment wherein a surface of the carrierbase is made a rough surface by forming a plurality of concavities isdescribed. The surface of the carrier base (the rough surface) is notlimited to one having a plurality of concavities. For example, thesurface of the carrier base can be made a rough surface by processingthe surface so that is has a plurality of convexities.

[0158] In the above, the specific embodiments of the wiring transfersheets of the present invention and methods for producing them have beendescribed. Next, a method for producing a wiring board using the wiringtransfer sheet of the present invention is described.

[0159] The wiring board of the present invention is one wherein a wiringlayer is formed by transferring a wiring layer of a wiring transfersheet of the present invention, and at least an exposed area of asurface of an electrically insulating substrate is a rough surface (therough surface of the electrically insulating substrate constituting aportion of a surface of the wiring board, which surface has the wiringlayer). The rough surface preferably has a plurality of convexities. Theelectrically insulating substrate on which the wiring layer is to betransferred is as described above, and contains, for example, athermosetting resin or a thermoplastic resin.

[0160] As described above, there are first and second methods forproducing the wiring board of the present invention. In the firstproduction method, the step of forming at least one of the wiring layerswhich are disposed on both surfaces of an electrically insulatingsubstrates includes (1) the step of superposing a wiring transfer sheetof the present invention on a surface of an electrically insulatingsubstrate, (2) the step of transferring a wiring layer of the wiringtransfer sheet to an electrically insulating substrate, and rougheningthe surface of the electrically insulating substrate so that the surfacehas a shape complementary to a rough surface of a carrier base of thewiring transfer sheet, and (3) the step of removing the carrier base ofthe wiring transfer sheet.

[0161] The wiring transfer sheet of the present invention is superposedon at least one of the surfaces of an electrically insulating substrate.In the production method of the present invention, an electricallyinsulating substrate having through holes filled with a conductive pasteis used. Upon superposing the wiring transfer sheet, it is necessaryalign the wiring layer to be transferred and the through holes filledwith the conductive paste so that a predetermined connection is obtainedthrough the electrically insulating substrate between the wiring layersdisposed on both surfaces of the electrically insulating substrate. Whenthe carrier base of the wiring transfer sheet is made from a materialthrough which a visible ray can pass, the wiring layer of the wiringtransfer sheet and the through holes of the electrically insulatingsubstrate are employed as alignment markers. These alignment markers arerecognized with one recognition system (e.g. a camera) from the upperside of the carrier base (that is, the opposite side to the surfacewhere the wiring layer is formed), whereby the alignment superposing iscarried out. The alignment markers recognition system may be one whichuses an X-ray.

[0162] In the case where the electrically insulating substrate containsan uncured thermosetting resin, the thermosetting resin is in an uncuredor a semi-cured state at the stage of superposing the wiring transfersheet to the electrically insulating substrate. This is for ensuringthat convexities complementary to the concavities formed on the wiringtransfer sheet are formed on the surface of the electrically insulatingsubstrate and ensuring the adhesion between the electrically insulatingsubstrate and another wiring board or another wiring board intermediatewhen the electrically insulating substrate is superposed on andintegrated with the other wiring board or the other intermediate ofwiring board.

[0163] After superposing the wiring transfer sheet on the surface of theelectrically insulating substrate, by heating and pressurization, thewiring layer is transferred while the surface of the electricallyinsulating substrate which contacts the exposed surface of the carrierbase of the wiring transfer sheet is made a rough surface which iscomplementary to the exposed surface (i.e. the rough surface) of thecarrier base. When a plurality of convexities are formed on the exposedsurface of the carrier base, convexities complementary to theconcavities are formed on the surface of the electrically insulatingsubstrate. The concavities are formed by a resin contained in theelectrically insulating substrate. Specifically, a thermosetting resincontained in the electrically insulating substrate is transformed to astate in which its viscosity is lowered by heating and pressurizationand enters the concavities in the carrier base followed by beingthermoset, whereby the convexities are formed. Further, this heating andpressurization compress the conductive paste within the through holes,whereby the wiring layer to be transferred is electrically connected toa wiring layer which is opposing through the electrically insulatingsubstrate. The condition of heating and pressurization are selectedappropriately depending on the kind of electrically insulating substrateand the wiring pattern and so on. Generally, heating and pressurizationare carried out by employing a temperature of between 150 and 250° C.and a pressure of between 1.96 and 19.6 MPa (between 20 and 200kgf/cm²).

[0164] It is necessary to carry out heating and pressurization in such amanner that the carrier base of the wiring transfer sheet is notcompatible with the electrically insulating substrate. For example, whenheating and pressurization are conducted so that the carrier base madeof a thermoplastic resin is softened, the resin constituting theelectrically insulating substrate and the resin constituting the carrierbase are mixed with each other, resulting in failure to form theconvexities complementary to the concavities of the carrier base, on theelectrically insulating substrate.

[0165] After transferring the wiring layer, the carrier base of thewiring transfer sheet is removed. The removal of the carrier base isconducted by an appropriate method depending on the material of thecarrier base. As mentioned above, in the case where the carrier base ismade of a metal which can be removed by selective etching, the carrierbase is preferably removed by etching. When the carrier base is made ofa resin, it is mechanically peeled off.

[0166] Further, in the first production method, the electricallyinsulating substrate may be superposed on a wiring board or a wiringboard intermediate which has already been produced, followed by beingadhered to the wiring board or the wiring board intermediate uponheating and pressurization, so that a multilayer wring board isobtained. The wiring board or the wiring board intermediate to which theelectrically insulating substrate is adhered may be any one, and doesnot necessarily need to be one wherein a wiring layer is formed bytransfer. The electrically insulating substrate may be superposed on adouble-faced wiring board or a multilayer wiring board whose wiringlayer is formed by a method other than transfer. Alternatively, theelectrically insulating substrate may be superposed on an intermediatedouble-faced wiring board or multilayer wiring board in which one ormore electrically insulating substrates contain an uncured thermosettingresin. In the case where the electrically insulating substrate issuperposed on an intermediate wiring board containing an uncuredthermosetting resin, the uncured thermosetting resin contained in theintermediate wiring board is also preferably post-cured in the step oftransferring the wiring layer.

[0167] In the above production method, a multilayer wiring board inwhich two or more wiring layers are formed with the wiring transfersheet of the present invention can be obtained by repeating the steps(1) to (3). In that case, since an exposed surface of the electricallyinsulating substrate on which the next electrically insulating substrateis superposed is made a rough surface (for example, a surface having aplurality of convexities), it adhere to the next electrically insulatingsubstrate well. Further, when the exposed surface of the wiring layer ismade a rough surface, the adhesiveness of the electrically insulatingsubstrate to the next electrically insulating substrates superposedthereon is more improved.

[0168] In the case where the steps (1) to (3) are repeated using anelectrically insulating substrate containing a thermosetting resin, itis preferable that in each step (2), heating and pressurization areconducted under the condition that the thermosetting resin contained inthe electrically insulating substrate is pre-cured (that is, thethermosetting resin is cured but not cured completely after itsviscosity has been lowered once). In the final step (2), heating andpressurization are carried out under the condition that thethermosetting resin contained in all the electrically insulatingsubstrates is post-cured. In other words, the repeated steps (2) exceptfor the final one are carried out under the condition that a) the wiringlayer of the wiring transfer sheet is temporarily adhered to theelectrically insulating substrate; b) the surface of the electricallyinsulating substrate is made a rough surface whose shape iscomplementary to the surface shape of the wiring transfer sheet; and c)the electrically insulating substrate is temporarily adhered to anotherelectrically insulating substrate which is located beneath theelectrically insulating substrate. Such a condition is more moderatethan that of post-curing the thermosetting resin, and is appropriatelyselected depending on the kind of thermosetting resin contained in theelectrically insulating substrate and the wiring pattern and so on.Generally, each step (2) (except for the final one) is repeatedemploying a temperature of between 50 and 100° C. and a pressure ofbetween 0.98 and 4.9 MPa (between 10 and 50 kgf/cm²).

[0169] In the final step (2), heating and pressurization are conductedunder the condition that the thermosetting resin contained in all theelectrically insulating substrates is post-cured together. The conditionis selected depending on the number of electrically insulatingsubstrates which have been superposed, and the degree of curing of thethermosetting resin contained in each electrically insulating substrate.Generally, in the final step (2), heating and pressurization areconducted employing a temperature of between 150 and 250° C. and apressure of between 1.96 and 19.6 MPa (between 20 and 200 kgf/cm²).

[0170] In the case where the post-curing is conducted after therepetition of temporary adhesion, the electrically insulating substratesare preferably superposed on both surfaces of the wiring board or thewiring board intermediate at the same time, that is, they are superposedsymmetrically. Of course, when a multilayer wiring board is produced byrepeating the steps (1) to (3) while superposing the electricallyinsulating substrates symmetrically, a circuit design is made so thatthe wiring board obtained by superposing the electrically insulatingsubstrates symmetrically, forms a circuit as desired.

[0171] The method for producing a multilayer board by repeating thesteps (1) to (3) may be carried out using an electrically insulatingsubstrate containing a thermoplastic resin. In that case, each step (2)(including the final one) is conducted under the condition that only theelectrically insulating substrate which is superposed on a wiring boardis softened. However, whether the thermosetting resin or thethermoplastic resin is a matrix component contained in the electricallyinsulating substrate, it is necessary that the conductive paste isdensified sufficiently to ensure a connection between the wiring layersin the wiring board which is finally obtained. Therefore, each step (2)needs to be conducted so that this requirement is satisfied in additionto the transfer of the wiring layer and the adhesion between the layers.

[0172] In FIGS. 8(a) to 8(c), the major steps of the first method forproducing a wiring board of the present invention are shown. FIG. 8(a)shows steps of superposing a wiring transfer sheet 803 on anelectrically insulating substrate 806 which is an object, andsuperposing the electrically insulating substrate 806 on a wiring board807.

[0173] The wiring transfer sheet 803 has the same construction as thatof the wiring transfer sheet 100 shown in FIG. 1. FIG. 8(d) is anenlarged view of Area A in the vicinity of a wiring layer of the wiringtransfer sheet 803. As shown, in the wiring transfer sheet 803,concavities 820 are formed on an exposed surface of a carrier base 801,and the interface between the carrier base 801 and the wiring layer 802is uneven.

[0174] The electrically insulating substrate 806 has through holes 804filled with a conductive paste 805. In the illustrated embodiment, theelectrically insulating substrate 806 is a composite containing anuncured thermosetting resin.

[0175] In FIG. 8(a), an All Layers IVH structure resin multilayer wiringboard is shown as the wiring board 807. The use of the All Layers IVHstructure resin multilayer wiring board makes a higher density wiringpossible. However, the structure of the wiring board 807 is not limitedto this. A glass-epoxy wiring board which is conventionally used may beemployed. Alternatively, an intermediate which has the same structure asthat of the wiring board 807 and contains an uncured thermosetting resinin a part of or all of the electrically insulating layers, may be used.

[0176] In the illustrated embodiment, the carrier base 801 is made froma material through which a visible ray passes (i.e. a transparentmaterial). Therefore, an alignment of the wiring transfer sheet 803 andthe electrically insulating substrate 806 is made using a recognitionsystem (not shown) which is disposed above the wiring transfer sheet803. An alignment of the electrically insulating substrate 806 and thewiring board 807 is made by registering the through holes formed foralignment in the substrate and the board.

[0177]FIG. 8(b) shows a step of heating and pressurizing the wiringtransfer sheet 803, the electrically insulating substrate 806 and thewiring board 807 in a state in which they are stacked. The step ofheating and pressurizing are carried out using, for example, a heatingplaten press. In this step, the resin component in the electricallyinsulating substrate 806 flows into the fine concavities 820 on thesurface of the wiring transfer sheet 803 and then the resin ispost-cured. Upon the post-curing, adhesions between wiring layer 802 andthe electrically insulating substrate 806, and between the electricallyinsulating substrate 806 and the wiring board 807 are made. Further, inthis step, the conductive paste 805 within the through holes 804 iscompressed, whereby the wiring layer 802 which is transferred from thewiring transfer sheet 803 and the wiring layer 808 on the wiring board807 are electrically connected. In the case where a wiring boardintermediate is employed in place of the wiring board 807, heating andpressurization are preferably conducted under the condition that anuncured thermosetting resin contained in the intermediate is post-cured.

[0178]FIG. 8(c) shows a step of removing the carrier base 801 of thewiring transfer sheet 803. As described above, the carrier base 801 isremoved by etching or by being mechanically peeled off, depending on thematerial thereof. FIG. 8(e) shows an enlarged view of Area C in thevicinity of the wiring layer in the wiring board 810 which is obtainedafter the carrier base has been peeled off. FIG. 8(f) shows an enlargedview of Area B, where a surface of the electrically insulating substrateis exposed on a surface of the wiring board 810. As shown in FIGS. 8(e)and 8(f), in the obtained wiring board, convexities are formed on thesurface of the wiring layer 802′ as well as the surface of theelectrically insulating substrate 806.

[0179] Next, in FIGS. 10(a) to (i), the major steps of the method forproducing a multilayer wiring board by repeating the step ofsuperposing, the step of heating and pressurization, and the step ofremoving the carrier base are shown. FIGS. 10(a) to 10(c) are the sameas FIGS. 8(a) to 8(c), illustrating steps for obtaining a wiring board1008, wherein the wiring layer 1002 is transferred to a surface of anelectrically insulating substrate 1006 using a wiring transfer sheet1000, while the electrically insulating substrate 1006 is adhered to asurface of a wiring board 1007, and then a carrier base 1001 is peeledoff. In FIG. 10(a), a wiring board intermediate which has the samestructure as that of the wiring board 1007, and which contains anuncured thermosetting resin in a part of or all of the electricallyinsulating layers may be used in place of the wiring board 1007.Alternatively, a wiring board intermediate which has another structuremay be used.

[0180] FIGS. 10(d) to 10(f) show steps for increasing the number ofwiring layers by one, wherein another electrically insulating substrate1016 is superposed on a surface of this wiring board 1008 and a wiringlayer is formed on a surface of the electrically insulating substrate1016. FIGS. 10(d) to 10(f) are the same as FIGS. 8(a) to 8(c),illustrating steps for obtaining a wiring board 1018, wherein a wiringlayer 1012 is transferred to a surface of the electrically insulatingsubstrate 1016 using a wiring transfer sheet 1010 while the electricallyinsulating substrate 1016 is adhered to a surface of the wiring board1008, and then a carrier base 1011 is peeled off. In the wiring boardthus obtained, convexities (not shown) are formed on the surface of thewiring layer and the electrically insulating substrate as shown in FIGS.8(e) and 8(f). The wiring layer 1002 and the wiring layer 1012 areelectrically connected by a conductive paste 1015 which is filled inthrough holes 1014 formed in the electrically insulating substrate 1016.

[0181] FIGS. 10(g) to 10(i) show steps for increasing the number ofwiring layers by one, wherein another electrically insulating substrate1026 is superposed on a surface of this wiring board 1018 shown in FIG.10(f) and a wiring layer is formed on a surface of the electricallyinsulating substrate 1026. FIGS. 10(g) to 10(i) are the same as FIGS.8(a) to 8(c), illustrating steps for obtaining a wiring board 1028,wherein a wiring layer 1022 is transferred to a surface of theelectrically insulating substrate 1026 using a wiring transfer sheet1020 while the electrically insulating substrate 1026 is adhered to asurface of the wiring board 1018, and then a carrier base 1021 is peeledoff. The wiring layer 1012 and the wiring layer 1022 are electricallyconnected by a conductive paste 1025 which is filled in through holes1024 formed in the electrically insulating substrate 1026.

[0182]FIG. 10 shows steps wherein three wiring layers are formed usingthe wiring transfer sheet of the present invention. Of course, morewiring layers may be formed by further repeating the same steps usingthe wiring transfer sheet of the present invention.

[0183] Alternatively, the steps shown in FIGS. 10(b) and 10(e) may becarried out, respectively, so that the temporary adhesion is madebetween the wiring layer and the electrically insulating substrate, andbetween the electrically insulating substrate and the wiring board. Thestep shown in FIG. 10(h) may be carried out so that the thermosettingresin contained in all the electrically insulating substrates 1006,1016, and 1026 is post-cured to integrate the substrates. In that case,the steps shown in FIGS. 10(b) and 10(e) do not necessarily need to becarried out using a heating platen press. For pre-curing thethermosetting resin, it suffices that heating and pressurization areconducted in such a manner that the thermosetting resin contained in theelectrically insulating substrate is pre-cured. Such heating andpressurization are, for example, thermal lamination. The steps ofremoving the carrier bases 1001 and 1011 shown in FIGS. 10(c) and 10(f)are preferably conducted by mechanically peeling off the carrier bases.If these carrier bases are removed by etching, uncured (i.e. notcompletely cured) thermosetting resin in the electrically insulatingsubstrates 1006 and 1016 may be dissolved because of being exposed to anetchant.

[0184] The final step of heating and pressurization, that is the step ofFIG. 10(h), is carried out under the condition that the thermosettingresin contained in all the electrically insulating substrates 1006, 1016and 1026 is post-cured while voids which exist between the electricallyinsulating substrates are eliminated. In the case where a wiring boardintermediate is used in place of the wiring board 1007 shown in FIG.10(a), the step of heating and pressurization are carried out so that anuncured thermosetting resin contained in the electrically insulatinglayer(s) of the intermediate is post-cured. Therefore, the step of FIG.10(h) is preferably conducted using a heating platen press by applying asufficient pressure over a sufficient time. Further, in the finalheating and pressurization step, the conductive paste within the throughholes formed in each electrically insulating substrate is compressedinto a high density, and thereby each electrical connection between thewiring layers becomes more reliable.

[0185] Next, the second method for producing a wiring board of thepresent invention is described. The second production method includes(1) the step of superposing an electrically insulating substrate on asurface of a wiring transfer sheet which surface has a wiring layer; (2)the step of forming through holes in the electrically insulatingsubstrate; (3) the step of filling the through holes with a conductivepaste; (4) the step of superposing the wiring transfer sheet on whichthe electrically insulating substrate has been superposed, on a wiringboard or a wiring board intermediate; (5) the step of heating andpressurization; and (6) the step of removing a carrier base of thewiring transfer sheet.

[0186] In the case where the electrically insulating substrate containsan uncured or semi-cured thermosetting resin, the step (1) ofsuperposing the electrically insulating substrate on the wiring transfersheet is carried out under the condition that the thermosetting resin ispre-cured so that the electrically insulating substrate is temporarilyadhered to the wiring transfer sheet. The temporary adhesion ispreferably conducted using a roll laminator within a short time so thatthe curing of the thermosetting resin is not promoted. If the curing ofthe thermosetting progresses too much, it is difficult to adhere theelectrically insulating substrate to the wiring board.

[0187] The step (2) of forming the trough holes in the electricallyinsulating substrate may be carried out by a conventional method, forexample a laser processing. The step (3) of filling the through holeswith the conductive paste may be carried out by a conventional method,for example, a screen printing of the conductive paste. By carrying outthe steps (1) to (3), a laminate wherein the electrically insulatingsubstrate is bonded to the wiring transfer sheet is obtained. Thelaminate of the wiring transfer sheet and the electrically insulatingsubstrate is more easily handled than only the wiring transfer sheet.

[0188] Next, the step (4) of superposing the laminate obtained bycarrying out the steps (1) to (3) on a surface of a wiring board or awiring board intermediate with the electrically insulating substrate incontact with the surface, is carried out. As described above inconnection with the first production method, upon this superposing step(4), it is necessary to make an appropriate alignment of theelectrically insulating substrate and the wiring board or the wiringboard intermediate. In the case where a visible ray passes through acarrier base of the wiring transfer sheet and the electricallyinsulating substrate, the alignment can be made using a recognitionsystem (for example, a camera) which is disposed on the wiring transfersheet side. In the case where a visible ray is difficult to pass throughthe electrically insulating substrate because the substrate containsfibers and so on, it is necessary to previously form through holes foralignment in the electrically insulating substrate of the laminate, andthe wiring board or the intermediate wiring layer.

[0189] After the wiring transfer sheet with the electrically insulatingsubstrate superposed thereon has been superposed on the wiring board,the step (5) of heating and pressurizing the entire laminate is carriedout. As described above in connection with the first production method,heating and pressurization are carried out by setting an appropriatecondition depending on the kind of electrically insulating substrate.This heating and pressurization transfers the wiring layer of the wiringtransfer sheet to the electrically insulating substrate completely, andmakes the surface of the electrically insulating substrate a roughsurface whose shape is complementary to a rough surface of the wiringtransfer sheet, and adheres the electrically insulating substrate to thewiring board.

[0190] After heating and pressurization, the step (6) of removing thecarrier base of the wiring transfer sheet is carried out. The removal ofthe carrier base is carried out by etching or mechanically peeling off,depending on the material of the carrier base.

[0191] The laminate obtained by carrying out the steps (1) to (3) may belaminated on a wiring board intermediate. In that case, in the step (5),heating and pressurization are preferably conducted so that athermosetting resin contained in the wiring board intermediate is alsopost-cured.

[0192] Also in the second production method, a multilayer wiring boardin which two or more wiring layers are formed with the wiring transfersheet of the present invention can be obtained by repeating the steps(1) to (6). Further, in the case where the steps (1) to (6) are repeatedusing an electrically insulating substrate containing an uncuredthermosetting resin, it is preferable that in each step (5), heating andpressurization are conducted so that the thermosetting resin containedin the electrically insulating substrate is pre-cured, but not curedcompletely. In the final step (5), heating and pressurization areconducted under the condition that the thermosetting resin contained inall the electrically insulating substrates is post-cured. The conditionof the repeated steps (5) (excluding the final one) and the condition ofthe final step (5) are as described above in connection with the step(2) of the first production method.

[0193] In FIGS. 9(a) to 9(f), the major steps of the second method forproducing a wiring board of the present invention are shown. FIG. 9(a)shows a wiring transfer sheet 903 of the present invention, and FIG.9(h) shows an enlarged view of Area A in the vicinity of the wiringlayer of the wiring transfer sheet. The wiring transfer sheet shown inFIG. 9(a) is the same as that shown in FIG. 8(a). Therefore, thedescription as to FIG. 9(h) is omitted since it is the same as FIG. 8(d)

[0194]FIG. 9(b) shows the step of obtaining a laminate 909 bysuperposing an electrically insulating substrate 904 on a surface of thewiring transfer sheet 903, on which surface a wiring layer 902 isformed. In the laminate 909, the electrically insulating substrate 904is temporarily adhered to the wiring transfer sheet 903. In theillustrated embodiment, the electrically insulating substrate 904 is acomposite containing an uncured thermosetting resin.

[0195]FIG. 9(c) shows the step of forming through holes 905 in theelectrically insulating substrate 904. The method for forming thethrough holes is as described above.

[0196]FIG. 9(d) shows the step of filling the through holes 905 with aconductive paste 906. At a stage where this step has been finished, theelectrically insulating substrate is in a state in which it canelectrically connect two wiring layers on both surfaces of thesubstrate.

[0197]FIG. 9(e) shows the step of superposing the laminate 909 on awiring board 907. In FIG. 9(e), an All Layers IVH structure resinmultilayer wiring board is shown as the wiring board 907. The wiringboard 907 may also be another wiring board. Alternatively, a wiringboard intermediate may be used in place of the wiring board 907. Thesuperposing step is carried out so that the wiring layer 902, thethrough holes 905 and the wiring layer 908 are appropriately aligned.

[0198]FIG. 9(f) shows the step of heating and pressurizing the laminate909 which is superposed on the wiring board 907. In this step, thethermosetting resin contained in the electrically insulating substrate904 is post-cured, whereby adhesions between the wiring layer 902 andthe electrically insulating substrate 904 and between the electricallyinsulating substrate 904 and the wiring board 907 are made. Further, inthis step, the resin component in the electrically insulating substrate904 flows into the fine concavities 920 on a carrier base 901completely, and then it is cured. Furthermore, in this step, theconductive paste 906 within the through holes 905 is compressed wherebythe wiring layer 902 of the wiring transfer sheet 903 and a wiring layer908 on the wiring board 907 are electrically connected.

[0199]FIG. 9(g) shows the step of removing the carrier base of thewiring transfer sheet 903. In FIG. 9(i), an enlarged view of Area B inthe vicinity of a wiring layer in a wiring board 910 thus obtained isshown. As shown in FIG. 9(i), in the obtained wiring board, a wiringlayer 902′ is buried in the electrically insulating substrate 904.Further, convexities are formed on a surface of the wiring layer 902′ aswell as a surface of the electrically insulating substrate 904.

[0200] Other electrically insulating substrate(s) and other wiringlayer(s) may be superposed on the wiring board 910 by repeating thesteps shown in FIG. 9(b) to 9(g). In that case, as described above withreference to FIG. 10, it is preferable that the step of FIG. 9(f) isrepeated under the condition that the thermosetting resin contained inan electrically insulating substrate is not completely cured (that is,it is pre-cured), and the final step of FIG. 9(f) is carried out underthe condition that the uncured thermosetting resin contained in allelectrically insulating substrates is post-cured. This makes it possibleto realize more precise wiring and correspondence of through holes.

[0201] As described above, in the case where the resin is post-curedtogether after repeating the temporary adhesions (i.e. pre-curing), theelectrically insulating substrates are preferably superposed on bothsurfaces of the wiring board or the wiring board intermediate at thesame time, that is, they are superposed symmetrically. Of course, when amultilayer wiring board is produced by repeating the steps (1) to (6)while superposing the electrically insulating substrates symmetrically,a circuit design is made so that the wiring board obtained bysuperposing the electrically insulating substrates symmetrically forms acircuit as desired.

[0202] In the production methods shown in FIGS. 8 to 10, a wiring layeris transferred to one surface of an electrically insulating substrate bysuperposing a wiring transfer sheet of the present invention on thesurface of the electrically insulating substrate. The wiring transfersheets of the present invention may be superposed on both surfaces of anelectrically insulating substrate as shown in FIG. 16. In that case, thewiring layers are transferred to both surfaces of the electricallyinsulating substrate.

[0203] As described above, a wiring board with a built-in component canbe produced using a wiring transfer sheet of the present invention.Thereinafter, a method for producing it is described with reference tofigures.

[0204] In FIGS. 11(a) to (l), the major steps of a method for producinga wiring board with a built-in component of the present invention areshown. FIG. 11(a) shows an electrically insulating substrate 1101. Inthe illustrated method, the electrically insulating substrate 1101contains a thermosetting resin as a resin component. The illustratedelectrically insulating substrate 1101 is obtained by covering both mainsurfaces thereof with cover films 1102 and then forming through holes1103 followed by filling them with a conductive paste 1104. The coverfilms 1102 serve as a mask upon filling the through holes 1103 with theconductive paste and serve to protect the surface of the electricallyinsulating substrate so that the conductive paste is not adheredthereto.

[0205]FIG. 11(b) shows the step of removing the cover films 1102 andthen superposing wiring transfer sheets 1100 on both surfaces of theelectrically insulating substrate 1101. This wiring transfer sheet 1100is one of the present invention, and is comprised of a carrier base 1105and a wiring layer 1106 that is formed in a desired wiring pattern on asurface of the carrier base. Therefore, the wiring layer 1106 ispreferably formed of a copper foil in which both surfaces are roughened.Therefore, it is ensured that the wiring layer adheres well toelectrically insulating substrates on both surfaces of the wiring layer.

[0206]FIG. 11(c) shows the step of heating and pressurizing the wiringtransfer sheets 1100 which are laminated on both surfaces of theelectrically insulating substrate 1101. Here, heating and pressurizationare carried out in such a manner that the thermosetting resin containedin the electrically insulating substrate is pre-cured and the wiringlayers are temporarily adhered to the electrically insulating substrate,whereby a wiring board intermediate 1300 is obtained. Such heating andpressurization can be conducted with a simple apparatus such as alaminator. When using a vacuum laminator which has a flat platestructure, heating and pressurization are carried out under a conditionof, for example, 0.98 MPa 10 kgf/cm²), 80° C., and 5 minutes. It shouldbe noted that when heating and pressurization are conducted under suchconditions, the conductive paste 1104 in the electrically insulatingsubstrate 1101 is not sufficiently compressed and the electricalconnection between the wiring layers is not ensured by the conductivepaste.

[0207]FIG. 11(d) shows the step of peeling off one of two carrier basesof the two wiring transfer sheets from the obtained intermediate wiringboard 1300, and superposing an electrically insulating substrate 1111 onthe exposed surface resulting from the peeling off. This electricallyinsulating substrate 1111 has through holes 1113 filled with aconductive paste 1114. This electrically insulating substrate 1111corresponds to one which is obtained by carrying out the same steps asdescribed with reference to Fig. (a) and then peeling off one of coverfilms. The electrically insulating substrate 1111 is disposed so thatthe surface exposed by peeling off is in contact with the electricallyinsulating substrate 1101.

[0208]FIG. 11(e) shows the step of heating and pressurizing thesubstrate 1111 which is superposed on the substrate 1101. The carrierbase 1105 and the cover film 1112 which are not removed from theelectrically insulating substrate 1101 and 1111 in FIG. 11(d), serve toprotect a laminate in this step. Heating and pressurization are carriedout under the same condition as that in the step of FIG. 11(c). Thiscondition is convenient because the cover film does not melt even if itis a PET or PEN film, which does not withstand a high temperature (suchas 200° C.). In the obtained laminate, the thermosetting resin containedin the electrically insulating substrate 1111 is pre-cured, and theelectrically insulating substrate 1111 is temporarily adhered to theintermediate 1300 of wiring board.

[0209]FIG. 11(f) shows the step of forming a component-receiving space1107 wherein the component is to be disposed. In the illustrated method,the component-receiving space is a through hole which penetrates theelectrically insulating substrates 1101, 1111. As a method for formingthe through hole, a punching process with a metallic die, a laserprocess and a router process may be employed. The carrier base 1105 andthe cover film 1112 provided on the surfaces serve as a protective filmduring processing.

[0210]FIG. 11(g) shows the step of arranging a wiring transfer sheet1110 with a component 1108 mounted on a surface where a wiring layer1116 is formed, on one surface of the laminate obtained in the step ofFIG. 11(f) so that the component is positioned in thecomponent-receiving space 1107. Further, in this step, a protectionsheet 1109 is superposed on the other surface of the laminate. In theillustrated method, a semiconductor chip is used as the component 1108,and this component is bare chip mounted, and an under fill resin isinjected to seal the area between the semiconductor chip 1108 and thewiring layer 1116. The components mounted on the wiring board are notlimited to this, and a chip component may be mounted. In the illustratedmethod, the protection sheet 1109 is the same as the carrier base 1115of the wiring transfer sheet 1110. Thereby, both sheets 1109 and 1115can be conveniently removed in one process.

[0211]FIG. 11(f) shows the step of heating and pressurizing a laminatewhich includes the wiring transfer sheet 1110 and the protection sheet1109. Heating and pressurization are preferably conducted in vacuumunder the condition that the resin component of the electricallyinsulating substrate 1111 flows and fills the component-receiving space.The condition of heating and pressurization may be a post-curingcondition for the thermosetting resin, or may not be the post-curingcondition for the resin as long as the condition allows the resincontained in the electrically insulating substrate to flow sufficiently.For example, when the heating and pressuring condition of 4.9 MPa (50kgf/cm²), 200° C. and one hour, which is a post-curing condition for theresin is employed, the resin is exposed to a temperature range at whichits viscosity is minimum before the resin is hardened, ensuring the flowof the resin. Further, when the resin is post-cured, the conductivepastes 1104 and 1114 in the electrically insulating substrates 1101 and1111 are also post-cured to ensure an electrical connection between thewiring layers. When both surfaces of each of the wiring layers 1106 and1116 are rough surfaces, the adhesion between the conductive paste andthe wiring layer become higher, improving the reliability of theelectrical connection.

[0212]FIG. 11(i) shows the step of removing the protection sheet 1109and the carrier base 1115. Wiring layers on both surfaces of the wiringboard 1400 that is obtained in this step are formed with the wiringtransfer sheet of the present invention, and have rough surfaces on bothsurfaces (that is, the surfaces of the wiring layers which are exposedafter the removal of the carrier bases are also rough surfaces).Therefore, both surfaces of the wiring board 1400 are rough surfaces asa whole.

[0213] The laminate shown in FIG. 11(i) serves as a wiring board if thethermosetting resin in the electrically insulating substrates ispost-cured in the final step of heating and pressurizing. However, inthe wiring board shown in FIG. 11(i), no wire exists on one of thesurfaces where the component receiving space 1107 has been formed (thatis, the lower surface which is opposite to the component in FIG. 11(i)).The area where no wire exists becomes a dead space when a component ismounted on the surface of the wiring board.

[0214] In order to eliminate this dead space, another electricallyinsulating substrate and another wiring layer are further formed asshown in FIGS. 12(a) to 12(c). FIG. 12(a) shows the step in which twoelectrically insulating substrates 1121 with through holes 1123 filledwith a conductive paste 1124 are prepared, and are superposed on bothsurfaces of the wiring board 1400 shown in FIG. 11(i) while wiringtransfer sheets 1120 are further superposed on the surfaces of theelectrically insulating substrates 1121. The wiring transfer sheet 1120is the same as that used in the step of FIG. 11(b), and is comprised ofa wiring layer 1126 and a carrier base 1125 whose exposed surface is arough surface. Here, the electrically insulating substrates aresuperposed on both surfaces of the wiring board in order to reducewarpage which is caused by shrinkage of the electrically insulatingsubstrate due to curing of the resin. The shrinkage due to curing of theresin is small, and the electrically insulating substrate may bedisposed on only one surface of the wiring board.

[0215]FIG. 12(b) shows the step of heating and pressurizing the wiringtransfer sheets 1120 and the electrically insulating substrates 1121which are stacked. Heating and pressurization are carried out under thecondition that the thermosetting resin contained in the electricallyinsulating substrate 1121 is post-cured. In the case where the wiringboard is produced as shown in FIG. 12, it is preferable that the wiringboard 1400 is obtained by carrying out heating and pressurization underthe condition that the thermosetting resin is pre-cured in the step ofFIG. 11(h). This is for obtaining a more favorable adhesion between thewiring board 1400 and the electrically insulating substrate 1121, andfor preventing warpage in the finally obtained wiring board.

[0216]FIG. 12(c) shows the step of peeling off the carrier base 1125 ofthe wiring transfer sheet 1120. As a result, the wiring board wherein adead space is eliminated is obtained, as shown in FIG. 12(c).

[0217] In the production method shown in FIG. 11, the step of FIG. 11(e)may be a step of transferring the wiring layer to the electricallyinsulating substrate 1111, wherein the cover film 1112 is peeled offfrom the electrically insulating substrate 1111. A wiring transfer sheetis superposed on the electrically insulating substrate, and then heatingand pressurization are carried out. By repeating the steps shown inFIGS. 11(a) to 11(e) while carrying out the step of FIG. 11(e) as thewiring transfer step, a multilayer board which has a desired thicknessdepending on the size of the built-in component, can be obtained.Further, in the case where the steps shown in FIGS. 11(a) to 11(e) arerepeated and both surfaces of the wiring layer are rough surfaces, thereliability of the electrical connection between the wiring layers whichis made by the conductive paste is improved. Furthermore, the use of thewiring transfer sheet of the present invention makes a surface of theelectrically insulating substrate a rough surface, for example a surfacehaving numbers of fine convexities. Therefore, it is possible to ensuregood adhesiveness of the electrically insulating substrate to the nextelectrically insulating substrate which is superposed thereon.

[0218] Further, FIG. 13 shows another embodiment of the method forproducing a wiring board with a built-in component, which is anapplication of the production method shown in FIG. 11. FIG. 13(a) showsa step of preparing two structures 1140 which are obtained by peelingoff the protective sheets 1109 after heating and pressurization in thestep of FIG. 11(h), and then superposing these on both surfaces of anelectrically insulating substrate 1131. The electrically insulatingsubstrate 1131 has through holes 1133 filled with a conductive paste1134.

[0219]FIG. 13(b) shows the step of heating and pressurizing thestructure 1140 and the electrically insulating substrates 1131 in astate in which they are stacked. Heating and pressurization are carriedout under the condition that the thermosetting resin contained in theelectrically insulating substrate 1131 is post-cured.

[0220]FIG. 13(c) shows the step of peeling off the protective sheet1109. As shown, in the obtained wiring board, two built-in componentsare stacked. The components may be different from each other. Further,in order to eliminate the dead space in the wiring board shown in FIG.13(c), another electrically insulating substrate and another wiringlayer are further superposed by carrying out the steps shown in FIG. 12.

[0221] Even when any of the production methods is employed, at least anexposed area of a surface of an electrically insulating substrate towhich the wiring layer is transferred, is made a rough surface (forexample, a rough surface with fine convexities) by forming a wiringlayer using a wiring transfer sheet of the present invention. The fineconvexities provide an anchoring effect when an electrically insulatingsubstrate is laminated thereon. Therefore, by using the wiring transfersheet of the present invention, a multilayer wiring board with abuilt-in component is obtained so that a good adhesion between theelectrically insulating substrates is ensured.

[0222] Alternatively, in FIG. 11(d), in place of the double-faced wiringboard, a laminate as shown in FIG. 9(f) may be superposed on anelectrically insulating substrate 1111, and then the steps shown inFIGS. 11(f) to 11(i) may be conducted in order. In that case, thecarrier base 901 shown in FIG. 9(f) serves to protect the laminate inthe step of FIG. 11(e). Alternatively, a wiring board with a built-incomponent can be produced by forming a space for receiving the componentin the laminate shown in FIG. 9(f), followed by superposing thislaminate on the wiring transfer sheet with a mounted component andintegrating them.

[0223] Each of the methods for producing a wiring board as describedabove with reference to FIGS. 8 to 13 is merely an embodiment of theproduction method of the present invention, and there are many othervariations. For example, in each production method, an electricallyinsulating substrate containing a thermoplastic resin may be used inplace of the electrically insulating substrate containing an uncuredthermosetting resin. For example, in FIG. 11, if such an electricallyinsulating substrate is used, the thermoplastic resin is softened andflows upon transferring the wiring layer of the wiring transfer sheetwith a mounted component, by heating and pressurization, so that theexposed surface of the electrically insulating substrate is made a roughsurface and the void around the component is filled. Further, in thecase where superposing an electrically insulating substrate andtransferring a wiring layer are repeated, all the electricallyinsulating substrates do not necessarily need to be made from the samematerial. For example, after a wiring layer has been transferred to anelectrically insulating substrate containing a thermoplastic resin, anelectrically insulating substrate containing a thermosetting resin maybe superposed on it.

What is claimed is:
 1. A method for producing a wiring transfer sheetcomprising a carrier base and a wiring layer formed on a surface of thecarrier base, the method comprising: superposing on a surface of thecarrier base a sheet of a wiring material having a first rough surfaceso that the first rough surface contacts the surface of the carrierbase; forming on the surface of the carrier base a second rough surfacecomplementary to the first rough surface of the sheet of the wiringmaterial; and forming a wiring layer with a predetermined wiring patternon the surface of the carrier base by etching the sheet of wiringmaterial.
 2. The method according to claim 1, wherein the first roughsurface is a surface having a plurality of convexities.
 3. A method forproducing a wiring transfer sheet comprising a carrier base and a wiringlayer formed on a surface of the carrier base, the method comprising:forming the wiring layer having a predetermined pattern on the surfaceof the carrier base; and roughening an exposed area of the surface ofthe carrier base on which surface the wiring layer is formed, using aroughing treatment.
 4. The method according to claim 3, wherein aplurality of concavities are formed on an exposed area of the surface ofthe carrier base by the roughing treatment.
 5. A method for producing awiring transfer sheet comprising a carrier base and a wiring layerformed on a surface of the carrier base, the method comprising formingthe wiring layer by depositing a metal on a rough surface of the carrierbase by metal plating.
 6. The method according to claim 5, wherein therough surface of the carrier base is a surface having a plurality ofconcavities.
 7. A wiring transfer sheet produced according to the methodof claim 1.